in costa rica unintentional injuries are the second cause of mortality in children under 5 years of age, with a ratio of 9.23 per 100000 inhabitants for the year 2004. hey are also the leading cause of loss of productive life years (337%)) for this age group. the objetive of this study was to determine the impact of this kind of injuries over the mortality of children under 5 years of age seen t the hospital nacional de ni？os (hnn) and to characterize this population. methods: we performed a case-ccontrol study pooling data on chilren aged 0-5 years who had been discharged from hnn with the diagnosis of unintentional injury from december 2001 to december 2004. all children who died from these injuries during this period constituded the cases and for each one we choose a control with the same age, sex and diagnosis discharged alive for this cause. results: there were 36 cases (ddeaths from unintentional injuries) 50% of each sex. motor vehicle related injuries and drownings were the leading causes of death. most of them were from san josé. there was no statatistical difference betwen cases and the controls in the mayority of variables. most of the deaths were during the summer and vacational months, beside 35% of them ocurred on weekends. most of the cases were admitted during the second shift (2pm-10pm) moreover the mayority of injuries (64%) took place at home (p<0.05). no supervision of children resulted to be risk factor for an unintentional injury ocurrence (p<0.05), but not for mortality. conclusion: the injury registry in costa rica is still very deficient,which makes difficult to carry out analitycal sutdies of prevalence of risk factors of unintentional injuries.