The authors’ effort to provide a wide overview of sleep medicine, however, ultimately limits the book’s usefulness. Rare and unusual diagnoses are covered, but the same succinct approach is applied to common disorders. For example, the authors describe recurrent (periodic) hypersomnia and catathrenia (nocturnal expiratory groaning), illnesses the average clinician will probably never encounter. Sleep apnea, both obstructive and central, makes up the bulk of clinical work, comprising perhaps four of every five referrals to a sleep center, but receives only 50 pages of compact description, roughly one-eighth of the book. Restless legs syndrome and periodic limb movement disorder, two other common entities, receive even less space. Insomnia is better covered, with separate chapters devoted to causes, clinical approach, and management, but it too receives less attention than its high incidence merits: 17 pages. The coverage of delayed sleep phase and other disorders of circadian rhythm is also thin.