It is well known that small intestinal carcinoid tumors may occur as solitary or multiple lesions. However, the biologic significance of multiple carcinoid tumors has not been clearly defined. The purpose of this study was to compare the clinical and pathologic features and prognosis of patients with solitary versus multiple carcinoid tumors of the ileum. Sixty-eight patients, including 50 with solitary and 18 with multiple carcinoid tumors, were included in the study. Hematoxylin and eosin-stained slides from routinely processed tumor resection specimens of the ileum were evaluated for a variety of histologic features such as tumor size, depth of invasion, tumor stage, and venous, perineural, and lymphovascular invasion. Follow-up and clinical data, such as patient age, gender, presenting complaints, presence of synchronous or metachronous malignancies, and presence of the carcinoid syndrome, were obtained and the results were compared between the two patient groups. Fifty patients with solitary carcinoid tumors (male/female ratio, 27:23) and 18 patients with multiple tumors (male/female ratio, 7:11) were identified. Patients with multiple carcinoid tumors were significantly younger than patients with solitary tumors at the time of diagnosis (55 years vs 63 years, p = 0.006). There was a high association between multiple carcinoid tumors and the carcinoid syndrome (4 of 18 vs 1 of 50, p = 0.004) as compared with patients with solitary carcinoid tumors. There was also an association between tumor multiplicity and venous invasion, but this relationship was not statistically significant (p = 0.07). The follow-up period was similar for both groups (mean 36 months, median 26 months, range 1–139 months). A significantly higher proportion of patients with multiple carcinoid tumors were either alive with disease or died of disease (56%) compared with those with solitary carcinoid tumors (18%, p = 0.002), and this relationship persisted in multivariate analysis (p = 0.02). Overall, no significant differences were observed between these two patient groups with respect to other clinicopathologic features such as tumor size, depth of invasion, presence of distant metastases, lymphatic or perineural invasion, or presence of an associated malignancy (p >0.05). In conclusion, we found that patients with multiple carcinoid tumors are younger, have a significantly greater risk of developing the carcinoid syndrome, and have a poorer prognosis than patients with solitary tumors.