In recent years it has been suggested that patients with celiac disease can be adequately followed up on the basis of merely clinical and serological response to a gluten-free diet. Thus, a duodenal biopsy some months after commencement of a gluten-free diet would no longer be necessary. We report here the case of a celiac patient in whom the ingestion of a milligram of gluten every day for 2 years prevented histological recovery in spite of satisfactory clinical and serological response. The literature regarding the minimal amount of gluten that could be harmless to celiac patients is reviewed.