Objective. To determine if there is an association between immunization with DTP and intersticial pneumonitis in post-mortem findings in infant deaths, between 2 and 6 months of age. Material and methods. An observational, descriptive, analytical case control study was carried out. The cases were children aged 2 to 6 months, who died in 2001 and 2002 with histopathology studies and a diagnosis of interstitial pneumonitis. The controls were children of the same age, who died in the same period, with a diagnosis other than interstitial pneumonitis. The odds ratio (OR) was used to analyze the strength of the association and logistic regression to make a multivariate analysis. Results. The sample was 25 cases and 52 controls. We found no association between vaccination with DTP and interstitial pneumonitis (p = 0.55). The variables associated with interstitial pneumonitis in the bivariate analysis were: dorsal sleeping position (OR = 3.74; p = 0.02), childbirth attended by gynecologist (OR = 3.14; p = 0.043), birth weight less than 3000 g (OR = 8.21; p = 0.001), hospital stay of 3 or more days (OR = 3.66; p = 0.009), diagnosis at childbirth (OR = 5.29; p = 0.008). The variables associated in the multivariate analysis were: birth weight less than 3.000 g (OR = 3.76; p = 0.038), diagnosis at childbirth (OR = 3.77; p = 0.048). Conclusion. There is no evidence of an association between the administration of DTP vaccine and interstitial pneumonitis. Interstitial pneumonitis was associated with other factors: birth weight less than 3.000 g and pathological diagnosis after childbirth.