Succinylcholine is a depolarizing neuromuscular blocker frequently used during electroconvulsive therapy. In most patients, the duration of paralysis is brief, allowing for spontaneous respiration shortly after the therapy. We report a case of delayed return of neuromuscular function after succinylcholine administered during electroconvulsive therapy in a 72-year-old man receiving cytarabine, vincristine, and rituximab chemotherapy for chronic lymphocytic leukemia. We hypothesize that an interaction between succinylcholine and one of the chemotherapeutic agents caused the prolongation of paralysis and believe that this is the first reported case of prolonged duration of succinylcholine following this regimen of chemotherapy. Despite this unexpected prolonged neuromuscular blockade, the patient could be treated uneventfully, with attention paid to his respiratory support and with subsequent succinylcholine dose titration to effect.