The prison environment represents a supplemental risk factor in the increased frequency of non-lethal self-harm among inmates, by comparison with the general population. The paper aims at defining the socio-demographic characters of those inmates who carried out the act by chemical means (drug intoxication or the consumption of other toxic substances) – classified as substance abuse, in contrast with the inmates who chose to act by physical means (plagues at various levels and/or ingestion of alien bodies). Between January 2009 – December 2009, 771 patients with autolytic acts were registered at the ER of the Sf. Ioan Emergency Hospital in Ia[i; 175 of these were inmates of the Ia[i Maximum Security Prison. The following variables were registered for all patients: sex, age, date of hospitalisation (the month and the day of the week are of special interest), time of the autolytic act, number of previous autolytic attempts, psychiatric disorders, method of choice, whether treatment was accepted or refused and whether the person needed hospitalisation or was treated as an outpatient. The data was processed by SPSS 10.0 for Windows. It resulted that the patients who had used mechanical means had a significantly higher average age, more frequent relapses, a maximum of hospital registrations in the months of May and February, and on Mondays. Self-injury by means of substance abuse was carried out by averagely younger patients, who had fewer relapse episodes, by whom the act was carried out most often in May and September, and on Saturdays. Regardless of the means chosen, most of these acts took place throughout the morning, when staff in charge with surveillance was present in the highest numbers. Given that numerous patients refuse treatment, or receive sufficient treatment as outpatients, the hypothesis takes shape that many of these acts are demonstrative.