Abstract The KEYNOTE-013 study was conducted to evaluate pembrolizumab monotherapy in hematologic malignancies; classical Hodgkin lymphoma (cHL) was an independent expansion cohort. We present long-term results based on >4 years of median follow-up for the cHL cohort. The trial enrolled cHL patients who experienced relapse after, were ineligible for, or declined autologous stem cell transplantation and experienced progression with or did not respond to brentuximab vedotin. Patients received IV pembrolizumab 10 mg/kg every 2 weeks for up to 2 years or until confirmed progression or unacceptable toxicity. Primary end points were safety and complete response (CR) rate by central review. Enrolled patients (N = 31) had received a median of 5 therapies (range, 2 to 15). After a median follow-up of 52.8 months (range, 7.0 to 57.6 months), CR rate was 19%, and median duration of response (DOR) was not reached; 24-month and 36-month DOR rates were both 50% by the Kaplan-Meier method. Median overall survival was not reached; 36-month overall survival was 81%. Six patients (19%) experienced grade 3 treatment-related adverse events (AEs); there were no grade 4 or 5 treatment-related AEs. With long-term follow-up among a heavily pretreated cohort, pembrolizumab had a favorable safety profile; some patients maintained long-term response with pembrolizumab years after end of treatment. This trial was registered at www.clinicaltrials.gov as #NCT01953692.