The prognostic significance of tumor infiltrating lymphocyte (TIL) response in cutaneous melanoma is controversial. This analysis of data from a prospective, randomized trial included patients with cutaneous melanoma > or = 1.0 mm Breslow thickness who underwent wide local excision and sentinel lymph node (SLN) biopsy. Univariate and multivariate analyses were performed to determine factors associated with TIL response, disease-free survival (DFS), and overall survival (OS). A total of 515 patients were included; TIL response was classified as "brisk" (n = 100; 19.4%) or "non-brisk" (n = 415; 80.6%). Patients in the nonbrisk TIL group were more likely to have tumor-positive SLN (17.6% vs 7%; P = 0.0087). On multivariate analysis, nonbrisk TIL response, increased tumor thickness, and ulceration were significant independent predictors of tumor-positive SLN. By Kaplan-Meier analysis, 5-year DFS rate was 91 per cent for those with a brisk TIL response compared with 86 per cent in the nonbrisk group (P = 0.41). The 5-year OS rates were 95 per cent versus 84 per cent in the brisk versus nonbrisk TIL groups, respectively (P = 0.0083). However, on multivariate analysis, TIL response was not a significant independent factor predicting DFS or OS. TIL response is a significant predictor of SLN metastasis but is not a major predictor of DFS or OS.