Background and Aims: There are concerns about the potential impact of the coronavirus disease (COVID-19) pandemic on substance use (SU) and other reinforcing behaviours (ORB). This paper investigates changes in SU and ORB among young men during the COVID-19 crisis (i.e. March-June 2020). Methods: Before and during the COVID-19 crisis, 2,344 young Swiss men completed questionnaires covering SU (i.e. alcohol, cigarettes, illegal cannabis), ORB (i.e. gaming, watching TV series, internet pornography) and sociodemographic and work-related characteristics (i.e. deterioration in the work situation, change in working hours, change in working hours from home, healthcare workers? and other professionals? contacts with potentially infected people, linguistic region, call up to military or civil protection unit, living situation, age). Results: Latent-change score models showed significant decreases of 17% for drinking volume and frequency of heavy episodic drinking, and a significant increase of 75% for time spent gaming and watching TV series. Subgroups showed greater relative increases. Frenchspeaking participants, those who experienced a deterioration in their work situation and healthcare workers in contact with potentially infected people reported increased cigarette use. Those without children increased gaming, whereas those who worked fewer hours, experienced a deterioration in their work situation or were French-speaking did more gaming and watched more TV series. Those who lived alone or were German-speaking watched more internet pornography. Conclusion: During the COVID-19 crisis, young Swiss men drank less alcohol and spent more time gaming and watching TV series. Changes in SU and ORB were not homogenous in the young Swiss men population.  Kulcsszavak: substance use, other reinforcing behaviours, COVID-19, cohort study on substance use risk factors, young men, Switzerland