OBJECTIVE To describe clinical findings and survival times for dogs with functional thyroid tumors treated with surgery alone and investigate potential prognostic factors for outcome in these patients. ANIMALS 27 client-owned dogs. PROCEDURES Medical records of 9 institutions were reviewed to identify dogs with hyperthyroidism secondary to thyroid neoplasia that were treated with surgery alone between 2005 and 2015. Data collected included signalment, hematologic and physical examination findings, tumor staging results, time from diagnosis to treatment, surgical procedure performed, histologic findings, evidence of recurrence or metastatic disease, and date of death or last follow-up. Median survival time and 1-, 2-, and 3-year survival rates were assessed by Kaplan-Meier analysis. Associations between variables of interest and the outcome of death were assessed with Cox proportional hazards models. RESULTS Dogs from 8 institutions met inclusion criteria. Median age at diagnosis was 10 years (range, 8 to 13 years). Golden Retrievers and Labrador Retrievers were commonly represented (5 dogs each). Polyuria with polydipsia (15/27 [56%]) and weight loss (12 [44%]) were the most common clinical signs; 2 dogs without clinical signs had hyperthyroidism identified by routine hematologic analysis. One dog had metastatic disease at the time of diagnosis. Most tumors (23/27 [85%]) were malignant. Estimated median survival time was 1,072 days. No significant prognostic factors were identified. CONCLUSIONS AND CLINICAL RELEVANCE Dogs with resectable functional thyroid tumors had a good prognosis with surgical excision alone. Survival times for these dogs were similar to those in previous studies that included dogs with nonfunctional thyroid tumors.