AIM:Schizophrenia (SCH) and bipolar affective disorder (BAD) are currently classified separately according to the DSM (The Diagnostic and Statistical Manual of Mental Disorders) and ICD (International Statistical Classification of Diseases and Related Health Problems) standardized diagnostic guidelines. However, the validity of this categorical approach is controversial because psychotic symptoms may be observed in both diagnoses. The purpose of this study was to compare the clinical and social characteristics in a sample group consisting of patients diagnosed with SCH or BAD to help demonstrate the basic difficulty in the current classification of SCH and BAD as two etiologically distinct diseases. SUBJECTS AND METHODS:The study sample group consisted of 102 patients diagnosed with SCH and 92 patients diagnosed with BAD. All of the participants were evaluated by Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition with regard to beginning symptoms of the disease, the symptoms and signs of active disease period within total disease duration, continuining residual symptoms in intermediate period. The patients were administered the Positive and Negative Syndrome Scale, the Quality of Life Enjoyment and Satisfaction Questionnaire and the Social Functioning Scale. RESULTS:The SCH and BAD groups in this study were statistically similar in terms of sex, length of education, age at disease onset, attempted suicide, quality of life and social functioning. CONCLUSION:Our study findings indicated that the course of disease in patients with BAD-1, in which psychotic features predominate and which exhibits a recurring course, shares various characteristics with SCH. It can be concluded that further phenomenological and neurobiological evaluations are required for intermediate cases with similiar clinical characteristics with schizophrenia and bipolar disorders.