A follow-up study was carried out in two localities in the semi-arid region of the State of Bahia, Northeast Brazil, with the aim of identifying the occurrence and nature of possible acute side effects subsequent to vitamin A megadose supplement given together with mass immunization in children 6-59 months old. The sample consisted of 852 children, 416 from the county of Teofilandia who received vitamin A together with vaccines and 436 from Santa Barbara, who received only vaccine. In the 24 hours before immunization, children from both groups had similar incidences of diarrhea, fever, and vomiting. Anorexia was more prevalent in Teofilandia and remained so throughout the study period. The results suggest that acute side effects like diarrhea, vomiting, fever, or anorexia were not associated with the vitamin A dosage given with mass OPV, DPT, and measles immunization.