Introduction: Subarachnoid hemorrhage (SAH) is associated with high morbidity and mortality. A certain degree of immunodepression has been reported during critical illness, and lymphopenia identified as an independent predictor of poor outcome; no data are available for critically ill SAH patients. We aimed to evaluate the prevalence of lymphopenia among SAH patients and its association with hospital-acquired infection.Methods: Retrospective cohort study of adult patients admitted to an intensive care unit with nontraumatic SAH between January 2011 and May 2016. Lymphocyte count was obtained daily for the first 5 days; lymphopenia was defined as lymphocyte count <1000/mm 3 . The occurrence of infection during the first 21 days after hospital admission, hospital mortality, and unfavorable neurological outcome (Glasgow Outcome Scale score 1 to 3 at 3 mo) were recorded.Results: Data from 270 patients were analyzed (median age 54 y; male 45%); 121 (45%) patients had lymphopenia and 62 (23%) patients developed infections. Median (25th to 75th percentiles) lymphocyte count at hospital admission was 1280 (890 to 1977)/mm 3 . Lymphopenia patients had more episodes of infection (38/121, 31% vs. 24/139, 17%; P = 0.003) than nonlymphopenia patients, while mortality and unfavorable outcome were similar. Lymphopenia was not independently associated with the development of infection, unfavorable neurological outcome or with mortality.Conclusions: Early lymphopenia is common after SAH, but is not significantly associated with the development of infections or with poor outcome.