Disadvantaged populations have an increased risk of suicide and suicide attempts because of the Covid-19 pandemic. To date, few studies focused on people living in detention, who have a high burden of mental health problems and are exposed to severe control measures. Our study investigated whether there was an increase in suicide attempts in prison. Data were collected in the largest Swiss pre-trial prison (Champ-Dollon) for the pre-pandemic and the pandemic periods. We identified a statistically significant 57%-increase of suicide attempts. Mitigation measures, access to mental health care, and access to vaccination are needed to protect this vulnerable population.