One of the elements of quality improvement of medication management services is measuring the quality of care and key performance indicators (KPIs) can be used in this assessment. There has been no publishing yet about a KPI instrument developed for ambulatory setting. To develop and validate KPI instrument for medication management services provided for outpatients in Brazilian context. A working group established 7 possible KPIs for assessment of the expert panel. For content validity, 16 experts were invited to participate in an internet based 2-round Delphi approach. Expert panel rated 7 possible KPIs using 7 attributes on a 5-point Likert scale for consensus. In order to construct validity and reliability, an internet questionnaire was developed for pharmacists that work in primary care to understand their views. In addition, a comparison between expert and pharmacist views about the indicators relevance was performed. Eleven (68.8%) experts participated in the Delphi round 1 and nine (81.8%) experts completed the 2 Delphi rounds. A new KPI was develop after expert panel assessment in the first round. Overall, content and construct validity were reached for 6 KPIs: pharmaceutical consultation provided (I1), pharmacist interventions accepted by the prescriber (I2), drug therapy problems resolved (I3), patient clinical status (I4), patient satisfaction (I5), and patient quality of life (I6). A set of 6 KPIs was developed for medication management services provided for outpatients. The instrument presented a good reliability and validity evidence. It is expected that these KPIs will improve the quality of medication management services.