ABSTRACT. Undernutrition may be an important modifiable risk factor for poor clinical outcomes in older individuals. To achieve earlier detection or prevention of undernutrition, more information is needed about risk factors for the development of undernutrition in community-dwelling older individuals. The objective was to identify early determinants of incident undernutrition in a prospective population-based study. Baseline data (1992–3) on socio-economic, psychological, medical, functional, lifestyle and social factors of 1120 participants aged 65–85 years of the Longitudinal Aging Study Amsterdam were used. Undernutrition, defined as a BMI < 20 kg/m2 or self-reported involuntary weight loss ≥ 5 % in the last 6 months, was assessed every 3 years during a 9-year follow-up period. Cox proportional-hazards regression analysis was used to investigate the association between early determinants at baseline and incident undernutrition. In 9 years, 156 participants (13·9 %) developed undernutrition. In univariate analyses, female sex, depressive symptoms, anxiety symptoms, multiple chronic diseases, high medication use (women), poor appetite, no alcohol use v. light alcohol use, loneliness, not having a partner, limitations in performing normal activities due to a health problem, low physical performance (participants aged < 75 years) and reporting difficulties walking stairs (participants aged < 75 years) were statistically significantly associated with incident undernutrition. In a multivariate model, poor appetite and reporting difficulties walking stairs (participants aged < 75 years) remained early determinants. The results of the present study can be used to identify subgroups of older individuals with increased risk of undernutrition and to identify modifiable determinants for the purpose of prevention of undernutrition.