Problems of drug availability and accessibility remain a major obstacle to the improvement of sanitary conditions in D.R. Congo, where rational drug use is a major concern. This study assesses prescriptions and cost related to the treatment of malaria and gastroenteritis in two hospitals of Kinshasa. The analysis of prescriptions shows that multiple drugs are prescribed, some of them very irrationally. Both factors increase of the cost of treatment. The lack of prescription policies, the shortage of diagnostic tools, the insufficient knowledge of pharmacology and therapeutics are, with economics constraints, key factors in this phenomenon. Training, education and sensitization of health professionals to the use of drugs are essential for improving the quality of and access to appropriate care.