The aim of this observational study was to assess rates of suicide and suicide attempts, in relation to gender, age, place of birth and security levels, in north-eastern Italian prisons during 2010–2016, and investigate associations with prison overcrowding, offence type and prior self-harm and suicide attempts. The study was based on individual data on suicides and suicide attempts from 16 prisons, with an average yearly number of 3900 inmates during the study period, for all prisons combined. Descriptive and binomial regression analyses were performed. Rates of suicide and suicide attempts in Triveneto prisons were 1and 15 per 1000 inmates, respectively. >90% of suicides and suicide attempters were men aged between 21 and 49 years old, and most had committed violent offenses. Only half the prisoners who died by suicide and 30% of those who made a suicide attempt in custody were Italians. ‘Cooperative witnesses’ had the highest mean suicide attempt rate (30/1000 inmates). Fourteen per cent of suicides and 19% of attempters had a prior history of suicide attempts and self-injury. In binomial regression analyses, predictors of suicidal behaviour were being a male inmate in standard security conditions, with a mean age of 30 years. The study highlighted that there is a need for suicide prevention policies in Triveneto; these should take into account predictors of suicidal behaviours and individual characteristics of suicidal inmates. More research is warranted in order to both evaluate the effectiveness of prevention plans and better assess risk of suicide in specific groups, such as cooperative witnesses.