A substantial proportion of schizophrenia patients also exhibit obsessive-compulsive symptoms (OCS). We sought to determine whether the revealed symptom dimensions in OCD exist in schizophrenia patients with comorbid OCD. One hundred and ten patients who met DSM-IV criteria for both schizophrenia and OCD were recruited. Exploratory factor analysis of the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) checklist was conducted. The inter-relationship between the resulting factors and schizophrenia symptom dimensions, as assessed by the Schedule for the Assessment of Positive (SAPS) and Negative (SANS) Symptoms, was examined. The principal component analysis of 13 Y-BOCS checklist categories yielded a five-factor solution and accounted for 58.7% of the total variance: (1) aggressive, sexual, religious obsessions and counting, (2) symmetry and ordering/hoarding compulsions, (3) contamination and cleaning, (4) somatic obsession and repeating compulsion, (5) hoarding obsession and checking/repeating compulsions. The Y-BOCS symptom dimensions did not correlate with schizophrenia symptom dimensions. The five symptom dimensions are comparable to those revealed in "pure" OCD, and suggest the involvement of universal mechanisms in the pathogenesis of OCD regardless of the presence of schizophrenia.