Pressure ulcers are a significant problem in Public Health. A pressure ulcer is a tissutal lesion caused by different mechanisms such as local pressure, rubbing and dampness. Their frequency increases with age, in hypo-mobile patients, both in hospital and domestic environments. The preminent role of prevention in reducing the incidence and severity of pressure ulcers is supported by many studies; prevention measures are based on frequent changes in the person's posture and/or on the use of alternating pressure mattresses Study objectives : to evaluate the use of alternating pressure mattresses in such patients in terms of : 1- risk factors for ulcer development (Braden); 2- duration (days) of mattress usage; 3- description and incidence of skin lesions at the beginning of the study; 4- any possible changes (improvement/progression) in such lesions when mattress use was suspended. Appropriate data forms were filled in by nurses at the beginning and at the end of mattress usage. A total of 1,959 persons used the alternating pressure mattresses: of these, 83.62% had a Braden scale rating from 6 to 12, and 43.62% suffered from ulcers. The ulcers improved in 54.62% of the patients, progressed in 7.6%