A high incidence of diphtheria cases in children in East Java province, Indonesia, has been observed since the beginning of this century. Despite many efforts, the outbreaks continue. This study aims to explain the high incidence of diphtheria in children in East Java province since 2013. This cross-sectional surveillance report-based study used data from 38 districts in East Java since 1 January 2013. Collected data included demographics, clinical information, additional examinations, immunization history, and close contact management. Over eleven years, there were 4009 diphtheria patients, of whom 2921 (72.86%) were under 18 years of age. Boys (59.77%) outnumbered girls, and the most common age category was >60–144 months (51.66%). Most cases had incomplete or zero immunization (76.16%). Tonsillopharyngeal diphtheria was the most common type (69.60%). The five top districts with the most cases were Surabaya, Sidoarjo, Kabupaten Blitar, Kota Malang, and Kabupaten Malang. The eleven-year case fatality rate (CFR) was 2.36% (69/2921). This study shows that diphtheria cases in children and adolescents in East Java have consistently been high, and low immunization coverage might still be the leading cause. There has also been a shift in the district distribution. Diphtheria outbreaks require complete and sustainable efforts, not just outbreak response immunizations.