Objective The present investigation was designed to explore the role and implications of both daytime sleepiness and fatigue in obstructive sleep apnea syndrome with respect to sleep, perceived health quality, and psychological functioning. Methods Our participants consisted of two groups: 124 older community volunteers who completed a polysomnographic sleep study and were diagnosed with sleep apnea, and 19 healthy controls. All participants completed self-report measures of sleepiness, fatigue, sleep quality, health quality, and psychological functioning. Results The apnea sample was divided according to clinically relevant cut-offs on sleepiness and fatigue. When those with mid-range scores were ruled out, the following groups remained: low sleepiness/low fatigue (LL, n=23), high sleepiness/high fatigue (HH, n=28), high sleepiness/low fatigue (HS, n=10) and low sleepiness/high fatigue (HF, n=13). The respiratory disturbance index did not differ significantly among these groups and only the two highly fatigued groups (HH and HF) experienced significantly lower average oxygen saturation than the control group. Analyses revealed that the HH group was significantly worse than the LL and control groups on most sleep, health quality, and psychological measures. On these same measures, the groups for whom fatigue was low (LL and HS), regardless of sleepiness, were similar to controls. Conclusion When patients with sleep apnea are classified into different sleepiness/fatigue categories, the results show that high fatigue is associated with more severe dysfunction than high sleepiness. The current debate on whether to treat apnea patients with low sleepiness needs to consider the impact of fatigue.