Obstructive sleep apnoea (OSA) is an increasing problem worldwide. Yet, a large number of patients may remain undiagnosed. Dentists could suspect OSA, but little is known about their knowledge and attitudes towards the topic. An email questionnaire was sent to dentists working in Helsinki Health Centre, Helsinki, Finland (n = 226). It consisted of demographic data, items on dentists' overall knowledge of OSA and factors associated with it, and their possibilities and willingness to take part in the recognition and treatment of OSA patients. Altogether, 70·9% (n = 134) of dentists eligible for the study completed the questionnaire. Of them, 79·1% (n = 106) were general practitioners and 20·9% (n = 28) dentists with specialty training. Continuous positive airway pressure (CPAP) (99·3%) and weight control (99·3%) were both generally acknowledged as effective methods to treat OSA. Regarding the efficacy of other treatment modalities, significant differences were found between general practitioners' and specialists' opinions. For example, mandibular advancement devices (MAD) were less often reported by general practitioners (69·8%) than specialists (89·3%) (P < 0·05). The possible risk factors, signs and symptoms, and consequences of OSA were overall well recognised regardless the years in dental profession, but specialists saw more often that nocturnal sweating (P < 0·01) and snoring (P < 0·05) may signify OSA. Dentists could play an important role in suspecting OSA, but they may need more education to cope with that.