To assess the qualitative characteristics of the prescription for chronic diseases and to select the most appropriate quality indicator, we evaluated 1588 drugs recorded in 549 forms for chronic prescription. 64.9% of the drugs were included in the Index Farmacològic, and the same rate in the Essential Drugs list of the WHO, 73.4% had a high intrinsic value (IV) and 80.7% were monocomponents. The male patients received more drugs included in the WHO list and with high IV, while patients older than age 65 years received more drugs with absent or unacceptable IV. A higher quality in the four indicators was found in the prescriptions from the CAP physicians than in those from specialists. The drug preparations with a not high IV more commonly prescribed belonged to the categories of cerebral and peripheral vascular therapy (16.2%), antacids and antiflatulents (9.3%), oral antidiabetics (8.4%), and antivaricose and antihemorrhoidal drugs (8.4%). It is concluded that the intrinsic value in the most adequate quality indicator for the prescription studies in primary care.