Abstract Background Teleworking gained ground in most workplaces, but questions remain about its impact on mental health. This research used data from the BELHEALTH cohort, a Belgian longitudinal wellbeing study, to investigate the relationship between the extent of telework and three mental health outcomes: anxiety, depression, and burnout. Methods In June 2023, the quarterly online survey assessed telework frequency (never, monthly, weekly, daily) as well as state of anxiety (GAD-7), depression (PHQ-9) and burnout (BAT-12). A complete case analysis (n = 2,303) of these cross-sectional data was performed with employed participants aged 18-65 years. Logit generalized linear mixed models were constructed, with the mental health outcomes as binary outcomes, telework as ordinal covariates, and occupation, type of job, as random effects. The anxiety, and depression models were controlled for geographical location, sex, age, and education confounders, whereas the burnout model was controlled only for sex, and education due to lack of observations. Results In this secondary analysis, we found that daily telework increased the odds of anxiety by 2.33 (95% CI [1.71; 3.17], p < 0.01), the odds of depression by 2.98 (95% CI [2.16; 4.12], p < 0.001), and the odds of burnout by 1.17 (95% CI [0.87; 1.58], p > 0.05) as compared with not teleworking while controlling for confounders. The category of monthly telework was associated with lower odds of anxiety (0.85; 95% CI [0.67; 1.07], p > 0.05), depression (0.91; 95% CI [0.74; 1.28], p > 0.05), and burnout (0.95; 95% CI [0.79; 1.15], p > 0.05) as compared to not teleworking. Conclusions Full-time teleworkers seem to have a higher odds for negative mental health outcomes. Future studies should focus on the long-term causal mechanisms that explain how telework intensity influences mental health to tailor and optimize current wellbeing initiatives at the workplace. Key messages • Our survey points out that full-time teleworkers seem to be at risk of mental health problems. • The frequency of telework has a mixed influence on mental health, indicating that different employees need tailored wellbeing initiatives.