The purpose of this study was to determine the relationship of ethnic identity to psychiatric diagnosis in white, black, Latino, and Asian clients of the Los Angeles County mental health system. The sample (N = 26,400) consisted of adult inpatient and outpatient clients seen in county mental health facilities between January 1983 and August 1988. Logistic regression analysis was used to determine the relationship of ethnicity to diagnosis in both outpatient and inpatient samples. The covariates included in the analysis were age, gender, socioeconomic status, and primary language. Ethnicity had a significant and consistent relationship to diagnosis in both outpatient and inpatient samples, with black and Asian clients having a greater proportion of psychotic diagnoses than whites, and Latinos a lesser proportion than whites. None of the covariates included in the analysis had a consistent relationship to diagnosis. Whites and Asians received more diagnoses of major affective disorders than blacks or Latinos; blacks and Asians received more diagnoses of schizophrenia and other psychoses than whites, and Latinos received fewer of these diagnoses than whites. Substance abuse was lower for Asians than for the other three groups. Based on the findings, it was concluded that there continues to be a difference in psychiatric diagnosis that is related to ethnicity. Clinical practice issues and recommendations for further research are considered in relationship to these findings.