AimsWhen patients are harmed by, or dissatisfied with, healthcare, only a minority will lodge a complaint or file a claim for compensation. This survey aimed to investigate complaint behaviour and inequalities in complaints using self-reports and hypothetical case vignettes.MethodsCross-sectional, web-based survey among 6755 Danish men aged 45–70 years (response rate=30%). Participants reported their lifetime complaint experience and the likelihood that they would complain in response to hypothetical case vignettes.ResultsOverall, 4.8% of participants had complained about healthcare. Predictors were younger age (OR 2.08, 95% CI 1.32 to 3.27, p=0.002 45–50 years compared with 65–70 years), chronic illness (OR 1.49, 95% CI 1.12 to 1.98, p=0.006), rural residence (OR 2.11, 95% CI 1.20 to 3.73, p=0.010 comparing least and most populated areas), high healthcare utilisation (OR 1.55, 95% CI 1.18 to 2.03, p=0.002 primary care, and OR 1.97, 95% CI 1.52 to 2.55, p=0.000 hospital care) and decreased agreeableness on the 10-item Big Five personality inventory (OR 0.91, 95% CI 0.83 to 0.99, p=0.034). Complaint experience was associated with increased wish to complain about the treatment in the hypothetical vignettes (p=0.006).ConclusionsRoughly 1 in 20 men reported having complained about healthcare. Complaints were more common among men who were younger, living in rural areas, diagnosed with chronic illness and high users of healthcare services. Prior complaint experience may be associated with a higher proclivity for complaining about future healthcare. Findings suggest differences in the way healthcare users respond to care experiences, pointing to the importance of aligning expectations and providing clear information about treatment options.