Our aim was to estimate the frequency of sleep apnea, non-restorative sleep, and insomnia and their association with demographic factors, lifestyle behaviors and co-morbid conditions in an at-risk population in Spain. A total of 1009 individuals with suspected Obstructive Sleep Apnea Syndrome (OSAS) completed a questionnaire and personal interview including demographic data, lifestyle behaviors, sleep-wake schedule, diurnal and nocturnal symptoms and also co-morbid conditions. Laboratory tests included lung function test, echocardiography, arterial blood analysis, total blood counts, and standard polysomnography for diagnosing sleep apnea. The frequency of OSAS, insomnia and non-restorative sleep was 88.5%, 16.76%, 59.72%, respectively. The frequency of OSAS was lower in females than in males (OR 0.33, 95% CI 0.20–0.56) whereas the frequency of insomnia was higher (1.95, 1.29–2.95). People in the 61–70 year group exhibited higher frequency of OSAS (3.81, 1.51–9.58) and also insomnia (1.85, 1.08–4.32), whereas the obese exhibited higher probability of OSAS (1.80, 1.15–2.81). OSAS was associated with snoring (7.95, 1.57–24.58), nocturia (1.80, 1.12–2.89), daily fatigue (1.89, 1.12–3.17), apathy (0.53, 0.30–0.89), memory loss (0.44, 0.26–0.73), and hypertension (2.60, 1.41–4.78). Insomnia was associated with esophageal reflux (1.78, 1.21–2.61), awakening (3.39, 2.19–5.22), apathy (1.68, 1.11–2.55), and memory loss (1.58, 1.06–2.35). Non-restorative sleep was associated with nocturia (1.43, 1.01–2.05), gastro-esophageal reflux (2.08, 1.31–3.31), diaphoresis (3.31, 1.88–5.83), awakening (1.41, 1.01–2.02), daily fatigue (2.09, 1.47–2.97), memory loss (2.23, 1.40–3.54), irritability (2.26, 1.59–4.03) and headache (2.57, 1.65–4.00). The frequency of sleep-related breathing disorders was high in our sample. Different factors seem to be associated with OSAS, insomnia or non-restorative sleep.