Since November 2014, the pentavalent (Diptheria+Tetanus+Pertussis and Hepatitis B and Hib or DTP-HBHib) vaccine has been integrated into the Iranian national vaccination programme. We conducted a prospective study in Zahedan in the southeast of the Islamic Republic of Iran to determine the incidence of adverse events following immunization (AEFI) with the pentavalent vaccine in children aged under one year. Using cluster sampling, 1119 children aged 2-10 months at 15 public health clinics were invited, through their parents, to participate in the study. The parents were trained to register and report any AEFIs in a questionnaire. They were instructed to return the child to the clinic for further examination by a physician if they observed any complications within 3 days of vaccination. The most commonly reported AEFIs were fever (50.94%), mild (41.46%) and severe (1.70%) injection site complications, persistent crying for 3 hours or more (1.88%), hypotonic hyporesponsive episode (0.36%), vomiting (1.88%), diarrhoea (2.95%), and sterile abscess (0.62%). There were no cases of convulsion, purulent abscess or rash. The work experience of vaccinators (OR = 1.85; 95% CI: 1.4-2.46) showed a significant statistical association with the incidence of mild local complications at the injection site. Those with a history of Bacillus Calmette-Guérin (BCG) lymphadenitis (OR = 3.89; 95% CI:1.04-14.49) had a higher risk of severe local complications at the injection site. The observed incidence of serious AEFIs following pentavalent vaccine injection in the study population was within the expected range. However, some of the relationships observed in this study require further research.