Objectives: Chemsex is a phenomenon highly relevant to public health concerns. Our primary aim is to describe the Czech chemsex scene regarding substances used, sexual behaviour, mental health, sexual life satisfaction, internalization of homonegative attitudes, and prevalent chemsex patterns.Methods: The data from the European Men Who Have Sex With Men Internet Survey (EMIS) 2017 were used. The mental health of chemsex users was assessed by the Patient Health Questionnaire 4 (PHQ4), internalized homonegativity was measured using the Short Internalized Homonegativity Scale. A sample of 87 men who have sex with men (MSM) chemsex users and a comparison group of 261 MSM were selected from the total sample of 1,688 respondents. Mann-Whitney and χ² tests were used to compare groups.Results: Active chemsex users made up 5% of the sample (87 of 1,688), with an average age of 37 years. Chemsex users were more likely to engage in condomless sex with non-steady partners (χ² = 46.8, p < 0.001), and had dramatically more STIs, such as HIV (χ² = 52.9, p < 0.001), HCV (χ² = 25.9, p < 0.001), and syphilis (χ² = 41.5, p < 0.001). Chemsex users frequently injected drugs (n = 19, 20%). More than half (n = 48; 55%) of chemsex users had sober sex in the last 4 weeks. Chemsex culture was associated with riskier substance use, both in terms of mode and frequency. The mental health of chemsex users in our sample did not differ significantly from the comparison group (χ² = 0.2, p < 0.7). Chemsex users did not conceal their sexual identity more often than the comparison group, on the contrary, 69% (n = 59) of them were out to most significant others, compared to 53% (n = 134) in the comparison group (χ² = 8.8, p < 0.05). In addition, we did not find differences in the degree of internalized homonegativity (χ² = 0.9, p < 0.4). Chemsex users were clearly and significantly more satisfied with their sex life than the comparison group (Mann-Whitney U test, p < 0.001).Conclusions: In our sample, chemsex use was not associated with a negative impact on health or wellbeing. Our results suggest that chemsex is not a homogeneous phenomenon. Many different patterns and subcultures exist, some of them are riskier, some safer than others.