Background: Chronic lymphocytic leukemia (CLL) is a hematologic disorder in dogs, but studies on prognostic factors and clinical outcome are lacking. In people, several prognostic factors have been identified and currently are used to manage patients and determine therapy. Objectives: The aim of the study was to determine if the immunophenotype of neoplastic cells predicts survival in canine CLL. Design: Retrospective study. Animals: Forty-three dogs with CLL. Procedures: Records of dogs with a final diagnosis of CLL were reviewed. For each included dog, a CBC, blood smear for microscopic reevaluation, and immunophenotyping data had to be available. Data on signalment, history, clinical findings, therapy, follow-up, as well as date and cause of death were retrieved. Results: Seventeen dogs had B-CLL (CD21+), 19 had T-CLL (CD3+ CD8+), and 7 had atypical CLL (3 CD3− CD8+, 2 CD3+ CD4− CD8−, 1 CD3+ CD4+ CD8+, and 1 CD3+ CD21+). Among the variables considered, only immunophenotype was associated with survival. Dogs with T-CLL had approximately 3-fold and 19-fold higher probability of surviving than dogs with B-CLL and atypical CLL, respectively. Old dogs with B-CLL survived significantly longer than did young dogs, and anemic dogs with T-CLL survived a significantly shorter time than dogs without anemia. Conclusions: Although preliminary, results suggested that immunophenotype is useful to predict survival in dogs with CLL. Young age and anemia are associated with shorter survival in dogs with B-CLL and T-CLL, respectively.