The prognostic value of the sentinel lymph node in Merkel cell carcinoma (MCC) has been examined previously in heterogeneous retrospective studies. The current retrospective study included a homogeneous population of patients with a localized MCC, all staged with sentinel lymph node biopsy. Factors associated with 3-year progression-free survival were analysed using logistic regression. The sentinel lymph node was positive in 32% of patients. The recurrence rate was 26.9%. In first analyses (n = 108), gender (p = 0.0115) and the presence of immunosuppression (p = 0.0494) were the only significant independent factors. In further analyses (n = 80), excluding patients treated with regional radiotherapy, sentinel lymph node status was the only significant prognostic factor (p = 0.0281). Immunosuppression and positive sentinel lymph node are associated with a worse prognosis in patients with MCC. Nodal irradiation impacts on the prognostic value of the sentinel lymph node status.