Background Second primary tumors (SPTs) are a common cause of reduced life expectancy in patients treated for head and neck cancer (HNC). This phenomenon forms an area to be addressed during posttreatment follow‐up. Methods We conducted a systematic review of literature following PRISMA guidelines, from 1979 to 2019, to investigate incidence of SPTs, synchronous, and metachronous, in HNC population. Results Our review includes data of 456 130 patients from 61 articles. With a minimum follow‐up of 22 months, mean incidence of SPTs was 13.2% (95% CI: 11.56‐14.84): 5.3% (95% CI: 4.24‐6.36) for synchronous SPTs and 9.4% (95% CI: 7.9‐10.9) for metachronous SPTs. The most frequent site for SPTs was head and neck area, followed by the lungs and esophagus. Conclusion Although with wide variations between studies, the rate of SPTs in HNC patients is high. Given the impact in the prognosis, we must develop strategies for the early diagnosis of SPTs.