The Parenting Stress Index was developed in response to the need for a measure to assess the parent-child system. Its abbreviated version, the Parenting Stress Index Short Form, is an instrument with multiple clinical applications and is useful for research and intervention purposes. The Parenting Stress Index Short Form was standardized for use with parents of children ranging from 1 month to 12 years old. Several validation studies are available, most of them not supporting the original structure of three factors. No validation studies for this instrument currently exist in Latin America for a socially vulnerable population. The purpose of this study was to evaluate both the validity and internal consistency of Parenting Stress Index Short Form in a Chilean sample including 336 dyads (mean age of mothers 21.4 years; SD = 7.38; and mean age of children 84.8 days; SD = 78.0), demonstrating risk for negative health outcomes and who attend public primary health care. An exploratory factor analysis showed a three-factor structure that was compatible with the original version and explained 41.45 % of the variance. Internal consistency was high both for the total scale (Cronbach’s α = 0.92) and the three subscales (0.81: Parenting Distress; 0.89: Parent–Child Dysfunctional Interaction and 0.88: Difficult Child). The Goldberg General Health Questionnaire was used to assess external criterion related validity and a positive and statistically significant correlation was found (0.86). The evidence suggests that the Parenting Stress Index Short Form can be used as an instrument to measure the relationship between parenting and stress. Due to its psychometric characteristics, it can be applied to a vulnerable Chilean population. The contribution of this study is the validation of this instrument in a Spanish speaking population with characteristics of social vulnerability.