Individuals with drug and alcohol problems often suffer from other physical and mental health problems as a result of drug or alcohol abuse. This article examined the morbidity of 52,200 individuals with alcohol or drug problems who were treated in all hospitals in Ontario during 1985 through 1986. The medical records of the patients with alcohol or drug diagnoses were compared with the medical records of all patients treated in Canadian hospitals in 1982. An age-sex standardization was used to determine excess or reduced morbidity in the sample. Standardized morbidity ratios were highest for individuals with a primary diagnosis related to licit drug use or misuse. Individuals with a primary diagnosis related to illicit drug use had intermediate standardized morbidity ratios, while individuals with a primary diagnosis related to alcohol use had the lowest standardized morbidity ratios. Alcohol and drug patients had the highest standardized morbidity ratios for mental disorders, infectious and parasitic conditions, and for injury and poisoning diagnoses. Future research should examine whether trends in excess or reduced morbidity in individuals with alcohol or drug diagnosis remain at the same level over time. Results of the study have implications for the improved measurement of health consequences associated with drug and alcohol consumption. Figures, glossary, references