Background In northern countries, suicide rates among prisoners are at least three times higher for men and nine times higher for women than in the general population. The objective of this study is to describe the sociodemographic, penal, health characteristics and circumstances of suicide of French prisoners who died by suicide. Methods This study is an intermediate analysis of the French epidemiological surveillance program of suicides in prison. All suicides in prison in 2017–2018 in France were included in the study. Archival sociodemographic and penal data and specific data on the circumstances of the suicidal act were provided by the National Prison Service. Health data was provided by physicians working in prison using a standardized questionnaire. Results In 2017–2018, 235 prisoners died by suicide. The suicide rate was 16.8/10 000 person-years. Among suicide cases, 94.9% were male, 27.2% were under 30, 25.1% were aged 30 to 39, 27.7% were aged 40 to 49 and 20.0% were 50 or older. At the time of suicide, 48.5% were on custodial remand. Incarceration is associated with a threefold increase in the frequency of anxio-depressive disorders (24.6% in prison versus 8.2% before prison). The week before the suicidal act, 60% of prisoners visited the health unit and a significant event was detected for 61% of all cases. Suicide was less than 1 week after prison entry for 11.9% of prisoners, corresponding to a suicide rate 6.4 (CI95% [4.3 – 9.5]) times higher than for the remaining time in prison, and was more than 1 year after entry for 33.7% of them. Conclusions The high frequency of events the week before suicide in our study suggests that events in prison could play a role in the occurrence of suicides. Comparative studies are needed to further explore the time association between events and suicide in prison. As most of prisoners who died by suicide visited the health unit the week before suicide, the identification of triggering factors could help psychiatrists and other health professionals to assess the short-term risk of suicide and to implement preventive measures.