Based in two Canadian male penitentiaries, this study explores the social organisation of prison tattooing, a widespread but under-researched practice identified in some epidemiological studies as a risk factor for Hepatitis C and HIV transmission. Qualitative and quantitative data are drawn from interviews with five incarcerated prison tattoo artists and 36 penal tattooing participants, who are also prison drug injectors, the sub-population known to report the highest prison tattooing rates. Unlike epidemiological studies, respondents' 'everyday knowledge' and experiential accounts illuminate the highest risk moments intrinsic to prison tattooing and possible points of intervention and advocacy for penal health care providers. The article argues for a sterile ('safe') prison tattooing programme to be available in prisons.