OBJECTIVE: To design and assess a model of risk sharing of pharmaceutical benefits in primary care based on allocating prescription budgets, assigning prescription quality standards and linking the results to an economical benefit. METHODOLOGY: In 1998 a prescribing budget was assigned to primary health care teams (PHCTs) of 22 basic health areas (BHAs) (488,900 inhabitants). The methodology for allocating drug budgets was based on the calculation of a maximum expenditure permitted (MEP) for each PHCT by assigning a percent increase above the previous year's expenditure, proportionally inverse to its cost/inhabitant. This cost/inhabitant was modulated by the percentage of population with free pharmaceutical coverage (population 65 years old or over and other specific population groups ) and the typology of the BHA (urban or rural). Prescribing quality standards (PQS) assigned for each PHCT consisted of the intrinsic pharmacological value (IPhV) of the prescription and the defined daily doses per 1,000 inhabitants per year (DHD) for anti-bacterial drugs and NSAIDs. Values for qualitative indicators were assigned depending on the distance between the PHCT's current value and the group average. Non-achievement of the objectives assigned for both MEPs and PQSs was linked to a loss of 2% of the total budget allocation contracted with the PHCT. RESULTS: The assesment of the prescribing budget objective showed that 36.4% of PCHTs had an expenditure below its MEPs and 63.6% over. Of PHCTs exceeding MEP, 42.9% presented a deviation of less than 5%, 28.6% between 5-10%, 21.4% between 10-15% and 7.1% greater than 15%. Qualitative evaluation showed that 86.4% of PHCTs achieved the objective of IPhV, 81.8% reached the DHD assigned for anti-bacterials and 68% the DHD for NSAIDs. CONCLUSION: The model has permitted the Catalan Health Service to implement the concept of risk sharing in the management of pharmaceutical benefits in primary care, and the introduction of greater accountability for prescription costs in general practice.