To demonstrate effectiveness of ambulatory health care plan implementation among institutions and variables associated with the differences observed. Randomized selection of primary health care (PHC) centers was done. Leadership ability of the plan manager was explored. Univariate/bivariate analyses were performed to observe correlation between variables. Two groups of PHC centers were established according to the efficacy of plan implementation: high and low performance. Differences between groups were observed (592%-1023% more efficacy in controls and practices; P < .001). Leadership was responsible for the main differences observed. Leadership of manager for implementation of the health care plan was the major important variable to reach the best efficacy standards.