Previous case reports have shown an association between acromegaly and the sleep apnea syndrome (SAS). Some of the patients described had central SAS, raising the possibility that an elevation of the growth hormone (GH) level may cause a defect in respiratory drive. We determined the prevalence of SAS in 21 patients with a history of acromegaly. We separated them into two groups based on serum GH concentrations. Ten patients had active acromegaly (mean GH concentration, 62.2 ng/mL; range, 12.6 to 148 ng/mL), while 11 patients had inactive acromegaly (mean GH, 3.2 ng/mL; range, 0.7 to 6.4 ng/mL). Four of the ten patients with active acromegaly had SAS; none of the 11 patients with inactive acromegaly had SAS. Three patients with SAS had the purely obstructive type, and one had the mixed central and obstructive type. The hypercapnic ventilatory response was normal in all patients tested and was not influenced by the GH level. We conclude that SAS is associated with active acromegaly and that the GH level does not affect the hypercapnic ventilatory response. The absence of SAS in successfully treated patients suggests that it may resolve after a normal GH level is restored.