A detailed nutrient assessment was made of 23 male and 24 female patients with Crohn's disease who entered sequentially into an outpatient clinic. Assessment included 48-hour dietary recall, anthropometric measurements, and biochemical and hematological tests appropriate to characterize protein-energy malnutrition. Approximately 40% of patients had energy intakes equal to only two-thirds of the Recommended Dietary Allowance (RDA). Three men and five women had relative body weights less than 85% of standard, but body weight was not correlated with energy intake. Relative body weight was correlated with arm muscle circumference in both male and female patients and with triceps skinfold and total lymphocyte count in women. Although the mean protein intake was greater than 150% of the RDA, evidence of protein malnutrition included low arm muscle circumference in 14% of the men and 15% of the women, low serum albumin concentration in 13% of the women, and low total lymphocyte count in one-half of the patients. The Crohn's disease activity index was correlated significantly with serum albumin, energy intake, and duration of disease in men and with serum ferritin and hemoglobin concentration in women. Thus, a reduced relative body weight or reduced serum albumin was not uncommon in patients with Crohn's disease but did not necessarily occur in those with reduced intakes of protein and energy. However, a low relative body weight may indicate need for further nutritional assessment.