Zinc deficiency is common in patients with Crohn's disease (CD), especially in those with skin lesions and growth retardation. Patients with fistulas have been considered to be another group with zinc deficiency. We therefore determined serum zinc concentrations of 50 patients with CD. Zinc deficiency was diagnosed in 17 out of 50 patients (34%). Serum zinc concentrations of patients with fistulas were significantly lower than those of patients without fistulas, and zinc deficiency was found in 11/17 (65%) patients. Zinc deficiency may play a role in the formation and clinical course of fistulas. Therefore, in view of possible therapeutic implications, determination of serum zinc concentration in patients with CD and fistulas appears to be of value.