There are different opinions about the cause of chronic psychiatric symptoms observed in drug abusers between Japanese and foreign psychiatrists. The Japanese seem to recognize the chronic psychosis as the result of drug abuse. In the other hand, foreigners diagnose these cases as dual diagnosis of drug abuse and psychosis. Authors studied the problem in this research. One of the authors has examined 120 inhalant abusers of all, in- and out-patients in Kanagawa Prefectural Center of Psychiatry, Serigaya Hospital from 1991 to 1995. These patients were classified into three groups: psychosis group (23 patients), dependence group (51 patients) and abuse group (46 patients) according to their clinical courses and psychiatric symptoms. The psychosis group consists of patients who showed psychiatric symptoms such as hallucination, delusion and thought disturbance for long time after detoxification. The dependence group contains patients whose inhalant dependence was severe and met DSM-4 Diagnostic Criteria for Substance Dependence, but manifested no chronic psychiatric symptoms after detoxification. The patients belonging to abuse group were at the earlier stages of inhalant abuse and had no chronic psychiatric symptoms. The average age of the first inhalant abuse was 14.7 years old in the psychosis group, 14.8 years in the dependence group and 14.7 years in the abuse group. The average years of abuse was 9.0 years in the psychosis group, and 8.5 years in the dependence group. There was little difference between these two groups. The psychosis patients manifested chronic symptoms 5.7 years on average after the first abuse of inhalants. About one forth (26.1%) of the psychosis patients and only 5.9% of the dependence patients had family history of schizophrenia. The difference was statistically significant. These results suggest that chronic psychiatric symptoms are caused not only by inhalant abuse, but also by the genetic factors of psychosis of each patient. There have been several reports that many patients with dual diagnosis of substance dependence and other mental disorders are poly-drug abusers. In our study, 43.4% of the psychosis group patients and 19.6% of the dependence group patients had the past history of abuse of other drugs including methamphetamine and marijuana. The difference was, however, not statistically significant.