Introduction:The COVID-19 pandemic drastically altered the way of life around the world. Due to social distancing measures, contact restrictions and fears of infection, social life has changed significantly. These measures along with the stressors associated with the current worldwide situation, will inevitably have an effect on people's interpersonal and personal behaviors. Aim: This study evaluates the effect the COVID-19 pandemic and nationwide German lockdown had on the sexual behavior of cis men. Methods: An anonymous nationwide web-based questionnaire was conducted among cis men in Germany during the first COVID-19 home isolation (April 20, 2020−July 20, 2020. The questionnaire was distributed via e-mail, online chats and social-media platforms. Main Outcome Measures: Data was collected on general characteristics including demographics and socio-economic backgrounds. To evaluate sexual health, questions from the Sexual Behavior Questionnaire were included. Results: 523 cis male participated. 414 met the inclusion criteria. Most were heterosexual (n = 248, 59.9%; vs homosexual n = 97, 23.4%; vs bisexual n = 69, 16.7%). 243 (59%) were employed, 153 (37.1%) were students and 16 (3.9%) were unemployed. Most of the participants reported an annual income lower than 75.000€. During the lockdown, average weekly frequency of sexual intercourse and masturbation was increased in all groups. Consistently, a significant rise of higher satisfaction with the frequency of sexual contacts during the quarantine was observed (P < .05). Furthermore, the level of sexual arousal increased significantly in all groups (P < .0005). Capability to enjoy sexual intercourse or masturbation increased significantly in heterosexual (P < .0005) and homosexual men (P < .005). Bisexual participants showed a significant increase in general satisfaction with sexual life (P < .05) and a significant decrease in satisfaction in relationship or single life (P < .05). Positive confounders in the changing of sexual behavior during the COVID-19 pandemic were: Being in a relationship or being single, parenthood and being employed. Conclusion: Our study firstly describes how COVID-19 pandemic related restrictions and social distancing measurements altered sexual behavior amongst cis male in Germany. Further studies, including sexual minorities specifically, are needed to clarify if the behavior in the first German nationwide quarantine has persisted or transformed as the pandemic proceeded.