BACKGROUND: Brachycephalic dogs display sleep-disordered breathing (SDB). The risk factors for SDB remain unknown. OBJECTIVES: To identify risk factors for SDB. We hypothesized that brachycephaly, increasing severity of brachycephalic obstructive airway syndrome (BOAS), excess weight, and aging predispose to SDB. ANIMALS: Sixty-three privately owned pet dogs were prospectively recruited: 28 brachycephalic and 35 normocephalic (mesaticephalic or dolicocephalic) dogs. METHODS: Prospective observational cross-sectional study with convenience sampling. Recording with the neckband was done over 1 night at each dog's home. The primary outcome measure was the obstructive respiratory event index (OREI). Body condition score (BCS) was assessed, and BOAS severity was graded for brachycephalic dogs. RESULTS: Brachycephaly was a significant risk factor for high OREI value (ratio of the geometric means 5.6, 95% confidence interval [CI] 3.2-9.9; P < .001) but aging was not (1.1, 95% CI 1.0-1.2; P = .2). Excess weight, defined as a BCS of over 5/9, (3.5, 95% CI 1.8-6.7; P < .001) was a significant risk factor. In brachycephalic dogs, BOAS-positive class (moderate or severe BOAS signs) was a significant risk factor (2.5, 95% CI 1.1-5.6; P = .03). CONCLUSIONS AND CLINICAL IMPORTANCE: Brachycephaly decreases welfare in a multitude of ways, including disrupting sleep. Brachycephaly, increasing severity of BOAS and excess weight are risk factors for obstructive SDB.