France currently has a very high level of prisoner suicides. Between 2005 and 2010, the mean annual rate was 18.5 suicides per 10,000 prisoners, seven times higher than for the general population. In this article, we begin by describing how suicide has changed since the mid-nineteenth century, highlighting the increasingly specific nature of suicide among prisoners versus non-prisoners. We then analyse the associations between individual characteristics and suicide risk, based on information from the French prison service’s database on all prison terms served in France between 1 January 2006 and 15 July 2009. Over this period, nearly 378,000 terms were observed (corresponding to more than 221,000 person-years) and 378 suicides were identified. Our results confirm the vulnerability of pre-trial detainees, and show that isolation, be it physical or social, is a key component of suicide risk, along with the type of offence resulting in imprisonment. Improving the conditions of detention is one of the priorities of prevention policies now being implemented, but the nature of the offence must also be taken into account as a suicide risk factor.