Siberian International Marathon (SIM) (Russian: Сибирский международный марафон) has been held in the city of Omsk since 1990, when the city was first opened to foreigners. The summer marathon is part of the City Days festivities. It takes place during the week of St. Ilya's Day, the patron saint of Omsk, in early August. The marathon itself takes place during the first Saturday of August. The winter half-marathon is during the January 7 Orthodox Christmas week.

Omsk is the administrative center and largest city of Omsk Oblast, Russia. It is situated in southwestern Siberia and has a population of over 1.1 million. Omsk is the third largest city in Siberia after Novosibirsk and Krasnoyarsk, and the twelfth-largest city in Russia. It is an important transport node, serving as a train station for the Trans-Siberian Railway and as a staging post for the Irtysh River.