At the request of Canadian health ministries, we reviewed recommendations in guidelines prepared by professional bodies on the referral of individuals to sleep laboratories. Searching electronic databases and the Internet, we found 37 guidelines that covered 18 applications of sleep laboratory investigation including obstructive sleep apnea, other respiratory disorders, obstructive sleep apnea and other conditions in children, sudden infant death syndrome, treatment for snoring, insomnia, depression with insomnia, narcolepsy, restless legs syndrome/periodic limb movement disorder, parasomnias and circadian rhythm disorders. We identified recommendations on referral of patients for sleep studies and assessed the quality and relevance of evidence cited in support of these. Of 81 recommendations, 46 were supported by evidence from primary investigations. Only six cases cited evidence from well-conducted, prospective controlled studies. Evidence was highly relevant in 18 cases, of some relevance in 22 and of little or no relevance in six. No evidence was provided in support of 31 recommendations, and in four cases the guideline had identified an absence of available evidence. Although the publications from professional bodies that were reviewed contain much detailed information, evidence supporting many recommendations is limited. There is a need for further, good quality, studies of many sleep laboratory applications.