BACKGROUND: Measles remains a significant public health threat in Uganda, with regular outbreaks. The current national immunization schedule offers the first measles-containing vaccine dose (MCV) at 9 months, and a second dose at 18 months. We investigated the epidemiology of measles in Ugandan children aged 18 months and younger. METHODS: We analyzed the national measles surveillance data from 2018 to the first quarter (Q1) of 2024, probing the demographic and geographic distribution. We categorized children as under 6 months, 6 to under 9 months, and 9-18 months. Suspected measles cases were classified as clinical, epidemiologically linked, laboratory-confirmed or discarded (not measles). RESULTS: 1316/2274 (57.9%) of the suspected cases were diagnosed with measles. One hundred and forty-nine cases (11.3%; 95% CI: 9.7-13.0) were aged under 6 months, 390 (29.6%; 27.0-32.0) 6 to under 9 months, and 777 (59.0%; 56.0-62.0) 9-18 months. 717/1208 (59.4%; 57.0-62.0) of vaccine-eligible children, with a captured vaccination history, had received at least 1 dose of MCV. 59.5% (95%CI: 55.0-63.0) of measles cases were unvaccinated vaccine-eligible children. Several districts did not achieve the WHO-recommended measles surveillance threshold of at least 2 discarded cases per 100 000 population. CONCLUSIONS: Most measles cases among Ugandan children ≤18 months are unvaccinated. Infants nine to 18 months old comprise most of the measles cases (59.0%; 777/1316). To achieve better control of measles transmission, review of the current vaccination policies with strengthened vaccination and surveillance systems are recommended.