Adolescent-onset cannabis use, compared with adult-onset use, has been associated with a higher risk for developing symptoms of schizophrenia-like psychotic disorders. To test the hypothesis that onset of cannabis use in early adolescence in male schizophrenia patients is associated with abnormalities in white matter structure and integrity, we used high resolution structural and diffusion tensor brain images to compare three groups of patients: those who started regular use of cannabis (1) before the age of 15 years (early-onset cannabis users, n = 10) or (2) at the age of 17 years or later (late-onset cannabis users, n = 8), and (3) those who were cannabis naïve (n = 8). To verify patient findings, we also compared white matter integrity of the three patient groups with that of a healthy control group (n = 10). Cannabis naïve patients showed reduced white matter density and reduced fractional anisotropy, an indicator for white matter integrity, in the splenium of the corpus callosum compared with patients with early-onset cannabis use. In the same brain area, cannabis naïve patients showed reduced fractional anisotropy compared with healthy controls. Our results suggest that the age of onset of cannabis use is not an identifying characteristic for white matter abnormalities in schizophrenia patients; however, our results might indicate a more vulnerable brain structure in cannabis naïve schizophrenia patients.