Underweight merupakan salah satu masalah gizi pada balita yang ditandai dengan nilai berat badan menurut umur (BB/U) kurang dari -2 standar deviasi berdasarkan Standar Pertumbuhan Anak WHO. Kondisi ini merefleksikan malnutrisi akut maupun kronis yang berdampak pada gangguan pertumbuhan, perkembangan kognitif, penurunan imunitas, hingga peningkatan risiko mortalitas pada balita. Provinsi Nusa Tenggara Timur tercatat sebagai salah satu provinsi dengan prevalensi underweight tertinggi di Indonesia berdasarkan Survei Status Gizi Indonesia (SSGI) 2024. Penelitian ini bertujuan untuk mengetahui faktor-faktor yang berhubungan dengan kejadian underweight pada balita usia 24-59 bulan di Provinsi Nusa Tenggara Timur. Penelitian ini merupakan penelitian kuantitatif dengan pendekatan cross-sectional menggunakan data sekunder SSGI 2024. Sampel penelitian berjumlah 7.895 balita usia 24-59 bulan di Provinsi Nusa Tenggara Timur. Analisis data dilakukan secara bivariat menggunakan uji chi-square dan analisis multivariat menggunakan regresi logistik ganda. Hasil penelitian menunjukkan prevalensi underweight pada balita usia 24-59 bulan di Provinsi Nusa Tenggara Timur sebesar 35,8%. Analisis bivariat menunjukkan bahwa terdapat hubungan yang signifikan antara berat badan lahir, riwayat ISPA, usia ibu saat hamil, tingkat pendidikan ibu, status pekerjaan ibu, jumlah anggota keluarga, pemberian PMT pemulihan, kepemilikan Buku KIA, sumber air minum layak, dan wilayah tempat tinggal dengan kejadian underweight (p < 0,05). Faktor dominan yang berhubungan dengan kejadian underweight pada balita usia 24-59 bulan di Provinsi Nusa Tenggara Timur adalah PMT pemulihan (aOR: 3,186; 95% CI: 2,614-3,884).

Underweight is a nutritional problem among infants and toddlers characterized by a weight-for-age (WFA) score of less than -2 standard deviations based on the WHO Child Growth Standards. This condition reflects both acute and chronic malnutrition, which can lead to growth failure, impaired cognitive development, weakened immunity, and an increased risk of mortality among infants and toddlers. East Nusa Tenggara Province is recorded as one of the provinces with the highest prevalence of underweight in Indonesia based on the 2024 Indonesian Nutrition Status Survey (SSGI). This study aims to identify factors associated with the incidence of underweight in infants and toddlers aged 24–59 months in East Nusa Tenggara Province. This is a quantitative study with a cross-sectional design using secondary data from the 2024 SSGI. The study sample consisted of 7.895 infants aged 24–59 months in East Nusa Tenggara Province. Data analysis was performed using bivariate analysis with the chi-square test and multivariate analysis with multiple logistic regression. The results of the study show that the prevalence of underweight among toddlers aged 24–59 months in East Nusa Tenggara Province is 35.8%. Bivariate analysis indicates a significant association between birth weight, history of acute respiratory infections (ARI), maternal age at conception, maternal education level, maternal employment status, household size, provision of recovery supplementary feeding (PMT), possession of a Maternal and Child Health (MCH) booklet, access to safe drinking water, and residential area with the occurrence of underweight (p < 0,05). The dominant factor associated with the prevalence of underweight among toddlers aged 24–59 months in East Nusa Tenggara Province is the provision of recovery supplementary feeding (aOR: 3.186; 95% CI: 2.614-3.884).