From an international comparison of arm anthropometric reference norms for the elderly a new diagnostic criterion for severe wasting malnutrition was derived: corrected arm muscle area at or below 16.0 cm2 for men or 16.9 cm2 for women. Of 201 consecutive hospital admissions aged 65 years and over, 10 subjects were malnourished according to this criterion. For each sex the malnourished group had lower weight, arm circumference and arm muscle area than the nonmalnourished group. Progressive decline of arm muscle mass during the study period was common in the malnourished groups. The diagnosis of severe wasting malnutrition had prognostic implications. Malnourished subjects had a much higher 90-day mortality than the 191 nonmalnourished subjects (50% versus 16.2%).