While the majority of the techniques and technologies used in the show are accurate and true to reality, the writers and crew readily admit that they "time cheat". Tests that take seconds in the show often take days or even weeks in real life.
Though not requested to do so by the producers, Marg Helgenberger attended actual autopsies over the course of the series for personal research purposes. The most 'memorable' aspect of the experience was the stench, according to Helgenberger's account on BBC's Breakfast (3 November 2011).
In July 2004, co-stars George Eads and Jorja Fox were fired (by direct order of CBS head Leslie Moonves) for breach of contract. CBS said that they were using delay tactics (refusing to show up for shooting) to force a pay raise at the beginning of the fifth season. They were soon rehired, but without a raise. They both denied that there was any contract dispute - Eads says he just overslept on the first day of production, and Fox said she didn't know about the letter of intent she reportedly failed to sign.
A fallout between George Eads and one of the female writers of the show prompted the absence of the actor for five consecutive episodes without explanation for the character on season 14, including the milestone 300th episode.
In real life, the Las Vegas Metropolitan Police Department (LVMPD) Crime Scene Investigators (CSI's) are not detectives and are called Crime Scene Analysts (CSA's). Most present day applicants are surprised to discover that the CSA's do not perform most of the tasks depicted on the series. E.g. They do not interview suspects, they do not write or execute search warrants, and they do not make arrests. In real life they are directed around the scenes by the detectives and supervisors, not the other way around. Detectives are commissioned police officers (sworn personnel). CSA's are civilian personnel, not sworn and do not have the same arrest powers as police officers. However they are very skilled technicians, and are a component of the police response to crime.
You often hear the characters referring to a four-nineteen (4-19,4/19, etc.) or sometimes a 4-45. These are the Las Vegas Metro 400 Event codes. The often-used 419 stands for "deceased person", while the less-used 445 is "explosive device threat".
Real life prosecutors have complained about something known as the "CSI Effect" where juries have unrealistic expectations about forensic science, either expecting copious amounts of forensic evidence in even routine cases or expecting an unrealistic level of accuracy and specificity from the tests presented.
At the conclusion of each case the culprits almost always confess their guilt to investigators that would most assuredly not be the people interviewing them, this helps to wrap up the case in a Scooby Doo like manner for the general viewing public.
The trivia items below may give away important plot points.
The oft-mentioned Tangiers Casino that was built and owned by Sam Braun in the series is completely fictional. There is no such casino in Las Vegas or anywhere else in the world. The name is often used by television shows and movies to bypass any potential copyright issues, or if a local casino doesn't give permission to use their name or likeness.
In response to a TV Guide interview that revealed Jorja Fox may leave CSI, fans began a "Dollar for Sense" campaign and sent over 2,000 dollar bills to CBS. The campaign also included three banner flyovers of CBS in Los Angeles, and flowers for her every day for a week.
William Petersen took a small leave of absence to perform on a Providence, Rhode Island stage during season 7, and the character of Michael Kepler (played by Liev Schreiber) was created to have a temporary replacement.
Grissom, et. al. use the Nikon F5 fitted with a multi-control back for photographing crime scene elements. As of the 5th season, this is no longer true. Most have different cameras: e.g. Warrick uses either a Nikon D70 or Nikon D100.