PURPOSE OF REVIEW: Whipple's disease (WD), triggered by Tropheryma whipplei ( T. whipplei ), is a rare, chronic, inflammatory, systemic infectious disease that typically manifests in adults. The most frequent initial manifestations include arthritis, followed by diarrhea, abdominal pain, and weight loss. Half the world's population is exposed to T. whipplei , but only one in a million develop WD. This suggests that acquired or inborn errors of immunity (IEI) may underlie WD. Anti-TNF treatment is a well established risk factor for flare-ups of WD. RECENT FINDINGS: We have also reported two rare IEI in patients with WD. Six WD patients from two unrelated kindreds were found to have autosomal dominant IRF4 deficiency acting via a mechanism of haploinsufficiency. These patients were otherwise healthy. In addition, a single patient with a history of WD and other infections was found to have autosomal recessive CD4 deficiency. SUMMARY: Rare IEI can underlie WD. Human genetic studies of patients with WD are warranted for the development of precision medicine for affected kindreds and to improve our understanding of the pathogenesis of this rare infectious disease.