This study aimed to assess the boundaries of the schizophrenia spectrum and whether inclusion of such phenotypes increases power for linkage analysis of schizophrenia. Participants were 234 first degree relatives (FDRs) of 94 schizophrenia probands in Northern Taiwan who completed a direct interview using the Diagnostic Interview for Genetic Studies (DIGS). Based on best estimate diagnosis, the morbidity risk in the relatives for schizophrenia was 2.5 percent (Weinberg's shorter method) or 3.9 percent (Kaplan-Meier estimate). Depending on the stringency of diagnosis, lifetime prevalence was 2.6 percent to 4.7 percent for schizotypal personality disorder, 3.4 percent to 8.6 percent for paranoid personality disorder, and 1.3 percent to 3.4 percent for schizoid personality disorder. These figures are significantly higher than the corresponding figures in the general population. However, none of the recurrence risk ratio for any spectrum that included both schizophrenia and a personality disorder (3.0 to 5.9) was greater than that of schizophrenia alone (9.3 to 14.4). Thus, including schizophrenia-related personality disorders in the spectrum did not increase power for linkage analysis of schizophrenia.