Background & aims: Malnutrition is widespread among older people and related to poor outcome. Reported prevalences vary widely, also because of different diagnostic criteria used. This study aimed to describe prevalences in several populations of older persons in different settings using harmonized definitions. Methods: Available studies within the Joint Programming Initiative (JPI) Knowledge Hub ‘Malnutrition in the Elderly’ (MaNuEL) were used to calculate and compare prevalences of malnutrition indicators: low BMI (<20 kg/m2; age-specific BMI <20 if age 65–<70 and <22 kg/m2 if age ≥70 years), previous weight loss (WL), moderate and severe decrease in food intake, and combined BMI <20 kg/m2 and/or WL in participants aged ≥65 years. Results: Fifteen samples with in total 5956 participants (59.3% women) were included: 7 consisting of community-dwelling persons, 2 studies in geriatric day hospitals, 3 studies in hospitalized patients and 3 in nursing homes. Mean age of participants ranged between 67 and 87 years. Up to 4.2% of community-dwelling persons had a BMI <20 kg/m2, 1.6 and 9% of geriatric day hospital patients, 4.5–9.4% of hospital patients and 3.8–18.2% of nursing home residents. Using age-specific cut-offs doubled these prevalences. WL was reported in 2.3–10.5% of community-dwelling persons, 6% and 12.6% of geriatric day hospital patients, 5–14% of hospitalized patients and 4.5–7.7% of nursing home residents. Severe decrease in food intake was recorded in up to 9.6% of community-dwelling persons, 1.5% and 12% of geriatric day hospital patients, 3.4–34.2% of hospitalized patients and 1.5–8.2% of nursing home residents. The criteria age-specific BMI and WL showed opposing prevalences across all settings. Compared to women, low BMI and moderate decrease in food intake showed low prevalences in men but similar prevalences were observed for weight loss and severe decrease in food intake. In half of the study samples, participants in a younger age group had a higher prevalence of WL compared to those of an older age group. Prevalence of BMI <20 kg/m2 and WL at the same time did not exceed 2.6% in all samples. The highest prevalences were observed based on combined definitions when only one of the three criteria had to be present. Conclusions: Prevalences for different criteria vary between and within the settings which might be explained by varying functional status. The criteria used strongly affect prevalence and it may be preferable to look at each criterion separately as each may indicate a nutritional problem.