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).
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.
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 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.
Following the departure of George Eads at the end of Season 15, only four members of the original cast remain: Jorja Fox (Sara Sidle), Eric Szmanda (Greg Sanders), Robert David Hall (Al Robbins), and David Berman (Dr. David Phillips). However, Eads was the last actor to depart who had remained in the main cast since the show's premiere.
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".
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 so 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.
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.
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.
The trivia item below may give away important plot points.
September 27th, 2015 is set to be the series finale of CSI. It will give a wrap up and answer questions for the fans of the show. William (Gil Grissom) and Marg (Catherine Willows) are set to return. After the series wraps up, Ted Danson (D. B. Russell) will then head to CSI: Cyber; the new CSI spinoff.