As part of safety monitoring during a group B meningococcal disease vaccination campaign in New Zealand, we examined the possible excess risk of vaccine-associated simple febrile seizures (SFS). We conducted a cohort analysis using data from active hospital-based surveillance in the South Auckland area and a national immunisation register. Based on analysis of approximately 63,000 doses, we found no statistically significant increase in SFS incidence within 1, 2, 4, or 7 days after vaccination for any/all doses administered to children aged 6 months through 4 years. We concluded that the vaccine is unlikely to induce a heightened risk of SFS.