Among the irrational factors involved in medical prescribing, few studies have investigated the problem of the 'pressure to prescribe'. The aim of the present work was to quantify this 'pressure to prescribe' and to investigate some potential predisposing factors. Each instance of a patient's behaviour suggesting 'pressure to prescribe' was registered for 599 outpatient general-practice clinics. 'Pressure to prescribe' was defined as each clear request by a patient that counteracted the diagnostic and/or therapeutic strategy of physicians. The study included 246 men and 356 women (mean age: 45.4 years). 'Pressure to prescribe' was found in 142 patients, i.e. 23.7% (95% confidence interval [CI]: 20.7-27.4%). Among patients aged >18 years, the percentage increased: 27.0% (CI 95%: 23.0-31.4%), i.e. 122 of 452 patients. 'Pressure to prescribe' was first observed with requests for drugs (17.3%), biological tests (2.5%), sick-leave from work (2.09%), radiological procedures (1.1%), medical certificates (1.0%), physiotherapy (0.8%), and referral to a medical specialist (0.3%). The drugs most often associated with 'pressure to prescribe' were analgesic (27.6%), nonsteroidal plus steroidal anti-inflammatory (17.1%), gastroenterological (16.2%), anti-infectious (14.3%) drugs followed by vitamins plus antiasthenic (11.4%), antiseptic (10.5%), nasal decongestant (9.5%), 'vasodilatory' plus 'veinotonic' (8.6%) drugs. Pressure to prescribe neuropsychiatric drugs involved only 7.5% of requests. Two predisposing factors were identified: age (with an increased 'pressure to prescribe' for older people) and, less importantly, female gender (women tended to exert more 'pressure to prescribe' than men). Analysis of 'pressure to prescribe' is an important topic in the area of Social Pharmacology.