BACKGROUND To analyze the main features of those patients admitted to the Hospital Detoxification Unit (HDU) and the environmental repercussions on them. MATERIALS AND METHODS We studied the patients admitted between April 91 and April 95, and revised their medical records with a protocol made for the occasion; the statistical measurements were subjected to the SPSS programme, using the Chi-square test and Fisher's test. RESULTS Of the 458 patients included in the study, 80% were males and the women showed a lower age average: 25.27 +/- 4.8 (p < 0.01); these women came from separated parents in 26 cases out of 79 (p = 0.03); and of the 130 patients whose siblings took drugs, 39 were females (p < 0.0007); of the 106 patients with a drug-dependent partner 62 were females (p < 0.00001), and this partner was infected in 22 cases (13 females: p < 0.0013); promiscuity/prostitution was present in 12 women out of 26 patients. 71 drank (21 females: p = 0.05). Only 41 patients had a steady job (40 males: p = 0.0009). 191 patients had been in prison, 116 of whom were males (p = 0.018) and 176 were awaiting trial, 102 of whom were given a therapeutic discharge (p = 0.05). Correlating the time of addition on admission to their age, the correlation rate is 0.58 (p < 0.00001). 291 patients had a therapeutic discharge and 29 were forced to leave, 28 of whom were males (p = 0.04). CONCLUSIONS The females in our sample are younger than the males and seen to be more influenced by environment, whereas the males show both a higher professional security and a higher criminal activity.