OBJECTIVE To determine the frequency of malignancy and survival rates of dogs that underwent splenectomy for incidentally detected nonruptured splenic masses or nodules. DESIGN Retrospective case series. ANIMALS 105 client-owned dogs. PROCEDURES Medical records of dogs that underwent splenectomy at a veterinary teaching hospital between 2009 and 2013 were examined to identify patients with incidentally detected nonruptured splenic masses or nodules without associated hemoperitoneum. Only dogs with histologically confirmed diagnoses were included. Information regarding signalment, preoperative diagnostic tests, perioperative blood product transfusions, splenic mass diameter, histologic findings, adjunctive treatments, and survival time was collected and analyzed. RESULTS 74 of 105 (70.5%) patients had benign splenic lesions and 31 (29.5%) had malignant neoplasia, most commonly hemangiosarcoma (18/31 [58%]). The hazard of death decreased as preoperative PCV increased; histopathologic diagnosis of malignant neoplasia was significantly associated with an increased hazard of death. Median life expectancy of dogs with benign and malignant lesions was 436 and 110 days, respectively; 41 of 74 patients with benign lesions and 3 of 31 patients with malignant neoplasia were still alive at study conclusion. Median life expectancy of dogs with hemangiosarcoma was 132 days; only 7 of these 18 dogs received any adjunctive chemotherapeutic treatments. CONCLUSIONS AND CLINICAL RELEVANCE Incidentally found, nonruptured splenic masses or nodules without associated hemoperitoneum were most commonly benign. Results suggested that life expectancy for these dogs with incidentally detected benign or malignant splenic lesions that received prompt intervention was better than has previously been reported for other studied populations.