The characteristics of synchronous and subsequent lesions of serrated adenomas (SAs) of the colorectum are still unclear. This study aimed to clarify the characteristics of synchronous and subsequent lesions of SAs compared with tubular adenomas (TAs) of the colorectum. Patients were divided into 2 groups: SA (127 patients) and TA (158 patients). The mean follow-up durations in the SA and TA groups were 39.7 and 42.7 months, respectively. The number and clinical features of the synchronous and subsequent lesions of both groups were examined. In the SA group, 19 (15%) patients had synchronous lesions and 3 (2%) patients had subsequent lesions. In the TA group, 68 (43%) patients had synchronous lesions and 14 (9%) patients had subsequent lesions. The frequencies of patients with synchronous and subsequent lesions in the SA group were significantly lower than those in the TA group (p < 0.0001 and p = 0.02, respectively). The most frequent synchronous lesion was SA (67%) in the SA group and TA (95%) in the TA group. The most subsequent lesion was SA (62%) in the SA group and TA (100%) in the TA group. The histology of the index polyp and synchronous and subsequent lesions tended to be identical. No invasive colorectal carcinomas were observed in either group. Our data suggest that the colonic tumorigenesis potential of patients with SA may differ from that of patients with TA.