During development, Herman van der Zwan, then head of John de Mol Produkties, asked his acquaintance Toots Thielemans if he would be interested in performing the title theme to Baantjer (1995). The famous Belgian mouth organ player came up with a theme he called "A Lonely Detective in Rotterdam". But since the series takes place in Amsterdam and the lead detective is happily married, Van der Zwan had to give Thielemans a few more pointers. Eventually the theme became known as "Circle of Smiles".
In later seasons, the amount of episodes was reduced for budgetary reasons and Piet Römer's advanced age. Seasons 1-5 had 13 episodes each. Starting with season 6, the amount was reduced to 10. In 2003, 13 episodes were shot for the 9th season. However, four of these were delayed and were eventually aired in the 10th season (2004), resulting in season 9 being the shortest season yet with 9 episodes. Eight episodes were shot for this season, giving a total of twelve episodes. However, four were delayed again, resulting in only 8 episodes. Two of these were pushed to the 11th season (2005), along with four new episodes to give a total of 6 - a record low. The other two, the two-parter ''De Cock en de afrekening'' were filmed in 2004 for season 10, but not aired until season 12 started in 2006. 6 new episodes were shot for season 12, giving 8 in total making it the only season with more episodes than its predecessor as opposed to less.
In spring 2007 RTL4 started airing episodes from the first few seasons on late Sunday evenings, advertising them as "Baantjer Classics". Each rerun was introduced by Piet Römer (playing De Cock). These reruns scored an average of 300,000 viewers, which was lower than any previous Baantjer airing, be it a rerun or a new episodes.
When Martin Schwab was going to leave after the 8th season in 2002 (he later reconsidered because Marian Mudder was also leaving), there were rumors that his character would be replaced by a new detective named Mulder, fresh out of the police academy. Some speculation hinted at Rick Engelkes being considered for the role, although this was never confirmed.
The real café where the scenes for Lowietje's café were shot was actually not located in a Red Light District ally. During filming, containers with fake brothels occupied by extras playing prostitutes were placed outside the café to create the illusion of an ally in the Red Light District.
Over the course of the series, Lowietje has been played by five different actors. Piet Kamerman, the last one, stayed over twice as long as all previous actors - a total of five seasons. He is the only actor to have played the role for more than two seasons.
Writer Appie Baantjer, who has close connections to the production team in order to make sure that they stay true to his characters, agreed to turn the character Prins, a man in the books, into a woman in order to "add a female element".
In order to make sure that all script writers kept the main characters consistent, a list of generic personal traits of the main characters, and their relationships with each other, was made in late 1994/early 1995. This document is often jokingly referred to as the "Character Bible".
In the first few seasons, De Cock always missed when throwing his hat onto the hat-stand. However, Piet Römer's hat throwing skills improved over time, and De Cock never misses anymore in newer seasons, with the exception of episode ''De Cock en de kroongetuige'' (# 11.2).
During filming of season 5 (1999), actor Freek van Muiswinkel (watchman Jochems) had to drop out due to illness (pancreatic cancer, which later led to his death). Panicked, the producers phoned Jeroen van Koningsbrugge, who had guest-starred as Jochems's assistant earlier in the season, asking him to play a replacement watchmen for the remainder of the season. A similar thing happened during filming of the 6th season (2000)- actor Hans Karsenbarg had to be admitted to the hospital. His friend Hans Veerman took over his role for the rest of the season.
In the Netherlands, the series (both reruns and new episodes) is always aired by RTL4 on Friday evenings, not counting airings on Belgian channels which are also received in the Netherlands. However, when live soccer matches threatened the viewing figures for some Baantjer reruns (which are known to usually score about as high as new episode, which is relatively unique), the series was temporarily moved to Tuesday evenings. Also, since late 2005, channel RTL7 also airs reruns of episodes on Saturday evenings (these are reruns of the episodes aired the Friday before; RTL7 is known for rerunning RTL4's programs the day after).
Due to its long run and self-contained episodes with very little continuity between them (besides two-parters), many guest stars portrayed multiple characters on the show. Also, some of the main and recurring cast portrayed other characters in guest appearances prior to joining the show as a regular: Kirsten van Dissel, Wimie Wilhelm and John Leddy.
Despite being based on the crime novels by Appie Baantjer, the show never adapted one of the novels. To date, the only direct film or series adaptation of a Baantjer novel is the feature film Moord in extase (1984).