A patient who presented with primary fibromyalgia syndrome (PFS) was found to have sleep apnea. Since frequent wakening and nonrestorative sleep are prominent clinical complaints in both disorders, we hypothesized an etiologic relationship. A subsequent clinical survey of 11 additional sleep apneics revealed that 3 (27%) fulfilled proposed criteria for PFS. This was significantly greater than local and literature reported studies of nonrheumatologic patients and was comparable to reported prevalence of fibromyalgia in rheumatologic referral populations. A blinded sleep physiology study of 7 patients with PFS revealed a significantly increased percentage of transitional sleep and increased frequency of miniarousals/h, but no significant evidence of occult sleep apnea compared to matched normal controls. The frequent arousals of sleep apnea may be associated with fibromyalgia in some patients but do not explain the sleep disorder of PFS.