OBJECTIVES: Many factors have been associated with the occurrence of constipation, particularly poor diet and lack of exercise. However, the importance of medications and general medical illnesses in constipation remains more uncertain. We aimed to identify risk factors for constipation from among patient clinical, therapeutic, and demographic characteristics. METHODS: The sample was composed of patients explicitly diagnosed with chronic constipation (n = 7251), those diagnosed with constipation of unspecified chronicity (n = 6441), and a sample of controls (n = 7103). All were drawn from a general practice research database representing more than 10 yr of data collection. RESULTS: A large number of clinical and therapeutic factors were independently associated with chronic constipation over and above age and gender. Primary neurological diseases were strongly associated with constipation but accounted for few cases. Opioids (OR = 1.6, population attributable risk [PAR] = 2.6%), diuretics (OR = 1.7, PAR = 5.6%), antidepressants (OR = 1.9, PAR = 8.2%), antihistamines (OR = 1.8, PAR = 9.2%), antispasmodics (OR = 3.3, PAR = 11.6%), anticonvulsants (OR = 2.8, PAR = 2.5%) and aluminum antacids (OR = 1.7, PAR = 3.0%) were associated with the highest risk among medications. CONCLUSIONS: Constipation is common in primary care, and multiple medications seem to be an important contributing factor. Concurrent diseases are also associated but at most are only contributing to a minority of cases.