Pascal Diethelm (born 1 December 1944) is a Swiss econometrician and tobacco control activist who is the president of the anti-smoking organization OxyRomandie.

At the WHO, he developed a database to monitor smoking prevalence rates around the world.

[3] In the 2000s, while working at the University of Geneva, Diethelm discovered that the Swedish scientist Ragnar Rylander had been serving as a secret consultant to the tobacco company Philip Morris since the 1970s.

Diethelm, along with his colleague Jean-Charles Rielle, were subsequently sued for libel by Rylander after they accused him of "scientific cheating without precedent".

The case was ultimately appealed to the Federal Supreme Court of Switzerland before finally being decided in Diethelm's and Rielle's favor.