Although the survival benefit conveyed by the automatic defibrillator has been well established for several subsets of patients, some patients who receive the device still die early. The relative lymphocyte count (%L), a portion of the white blood cell count differential, which is decreased in states of excess systemic stress, has prognostic value in patients with coronary artery disease and advanced heart failure. This study assessed the association of %L with survival in patients receiving automatic defibrillators. A total of 136 consecutive patients (81% men; mean age 64 +/- 12 years) who were using automatic defibrillators were followed for 29.6 months. The mean ejection fraction was 0.36 +/- 0.17, the mean %L was 22.7 +/- 8%, and 55 (40%) patients had decreased %L (< 20.3%). There were 20 deaths, for a 4-year survival of 71.5%. The association of %L with time to death was assessed by Cox proportional hazards analysis. Ejection fraction (P = 0.005), %L (P = 0.01), and diagnosis (P = 0.03) were independently associated with time to death on multivariate analysis. One-year and 4-year survival rates were 93% and 54%, respectively, for the 55 patients with abnormal %L, compared with 99% and 84%, respectively, for the 81 with normal %L (P = 0.03). This suggests that the %L is a readily accessible prognostic marker in patients using automatic defibrillators. This association is independent of age, sex, diagnosis, and ejection fraction.