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Impaired vigilance performance has been reported in older subjects with sleep apnea syndrome (SAS). The current study is an attempt to extend these findings and to investigate additional factors that might have implications for vigilance in the older adult. Fifty-nine older adults [age: 62 +/- 5 (mean +/- SD), range 54-75 years; respiratory disturbance index (RDI): 8.8 +/- 14.4 (mean +/- SD), range 0-67.5] were categorized as SAS or NotSAS, based on various classification criteria [i.e. apnea index (AI) > or = 5, and 10, RDI > or = 5, 10 and 15], and were compared on their vigilance performance as assessed by the computer program "Steer Clear". Vigilance performance did not discriminate the groups, independent of how they were formed. Groups were then formed based on vigilance performance (HiVig vs. LowVig) and compared on assorted sleep variables, periodic leg movements, and self-reported hypersomnolence and depression. Only age discriminated vigilance performance (an inverse relationship), accounting for 31% of the observed variance. Our findings suggest that subject selection may unintentionally bias findings regarding the neuropsychological functioning of individuals with SAS, that vigilance may be impaired only in relatively more "severe" SAS, and that severity of SAS in older adults may not be well characterized by current classification standards. Age clearly impacted vigilance performance, despite the constricted age range sampled, and should be taken into account in future research.