This is a case description of two patients with bipolar affective disorder, who presented complications, possibly due to underlying, undiagnosed obstructive sleep apnea syndrome (OSAS), during anesthesia for electroconvulsive therapy (ECT). The first patient, just after receiving the second ECT, developed tachypnea with spasm of the upper airways and severe oxygen desaturation He was intubated and transferred to the medical intensive care unit where he was extubated 15 h later. The second patient, just after the eighth ECT, developed tachycardia and severe hypertension. He was transferred to the recovery room where he received oxygen therapy via nasal cannula and amlodipine. Both patients in the diagnostic polysomnographic tests which followed revealed a moderate to high apnea - hypopnea index (AHI) and distortion of sleep architecture. These cases highlight the need to assess for OSAS patients who receive ECT, especially if they exhibit peri-anesthesia complications.