To evaluate the effect of a quality-monitoring program on the occurrence of sentinel events and on attitudes and behaviors of personnel's responses in a Non-Governmental-Organization (NGO).Between 1998 and 1999, a quasi-experimental design of the before-after type was conducted in 13 NGO clinics. Analysis of changes in attitudes and behaviors consisted in differences of means and analysis of variance between groups.The number of sentinel events decreased from 32 events detected before the quality-monitoring program to only 2 after it. Attitudes and behaviors improved, with differences of means of +1.1 and +1.2 (p < 0.05).The quality-monitoring program achieved the expected effects. It is noteworthy that attitudes and behaviors to prevent the occurrence of sentinel events were more prevalent after the intervention.