Oral diseases, mainly tooth decay and periodontal disease, are among the most common conditions in the world. The tooth decay is very prevalent in developing countries and particularly in disadvantaged backgrounds where insecurity and its corollaries prevail. Thus, our study focused on one of these places: the prisons, characterized by deprivation of liberty, monotony, boredom, and the difficult conditions of detention, brief by a total dependence of the detainee. The aim of this study was to determine the DMFT (Decayed, Missing, Filled Teeth) in detainees dwelling in prisons in Dakar. This cross sectional study included 754 detainees aged 18 years and more with a stay exceeding more than a year, in one of the four main prisons of the capital city, Dakar. The majority of detainees was males (90%), aged between 18 and 35 years (63%) and was staying at "Camp penal" (65%). The proportion of inmates with at least one tooth cavity was 81.3%, those with teeth sealed was 26.1% and the prisoners with missing teeth reached 70.6%. The highest average DMFT was noted at "Camp penal" (7.3) among men (6.5) and among inmates aged 36 to 45 years (6.1) with a significant difference. The tooth decay is particularly worrying in the prison population, hence the urgency to establish a programme of prevention and care of oral diseases in this environment.