Our aim was to describe the prevalence of disease-related undernutrition (DRU) on admission to a department of surgery in Suriname and to explore its association with ethnicity and adverse outcomes. All patients 18 years or older who were not pregnant were invited to participate. Data were collected on weight (history), length, fat-free mass index (FFMI) using bioimpedance analysis, and ethnicity. Age, sex, and diagnosis data were extracted from the medical files. Associations between DRU and ethnicity, functionality, and length of hospital stay were assessed using logistic and Cox regression analyses adjusting for age, sex, diagnosis, and disease severity. The study population of 351 participants revealed 46% were undernourished, 31% had unintended weight loss (UWL), and 27% had a low FFMI. DRU and low FFMI were associated with low handgrip strength, but UWL was not. DRU, UWL, and low FFMI were associated with length of stay. Determinants of DRU seemed to vary between ethnic groups. The prevalence of DRU was high, and nutrition protocols should be implemented to increase awareness and limit adverse outcomes. Further research is needed to reveal whether ethnicity should be part of the DRU risk assessment.