Genetic and environmental factors have been implicated in the etiology of nasopharyngeal carcinoma (NPC), a tumor known to be closely associated with Epstein-Barr virus (EBV) infection. Studies have reported familial aggregation of NPC and have suggested the possible aggregation of NPC and other cancers. We evaluated familial aggregation of cancer in 358 high-risk families with two or more NPC cases enrolled in a NPC genetics study in Taiwan. Participants were linked to the Taiwan National Cancer Registry to identify incident cancers diagnosed after study enrollment (started in 1996) and before December 31, 2005, or death. In total, 2,870 individuals from the NPC Multiplex Family Study contributed 15,151 person-years over an average of 5.3 years of follow-up. One hundred ten incident cancers were identified. Multiple-primary standardized incidence ratios (MP-SIRs) were computed to evaluate overall cancer risk associated with infectious agents and with other tumors. The overall MP-SIR was 1.3 (95% CI: 1.1-1.6), which was largely explained by an excess in NPC (MP-SIR = 15; 95% CI: 10-23). Exclusion of incident NPC diagnoses led to an overall MP-SIR of 1.0 (95% CI: 0.83-1.3). Similarly, the observed excess risk of cancers associated with infectious agents (MP-SIR = 2.0; 95% CI: 1.5-2.6) was driven by the excess in NPC; exclusion of NPC cases led to a reduced MP-SIR that did not differ from 1.0. Analysis of the largest NPC multiplex family study to date confirms the presence of coaggregation of NPC within families in Taiwan but does not provide evidence for a broader familial syndrome involving NPC and other tumors.