RATIONALE: Castleman disease (CD) is a rare disorder characterized by nonspecific clinical presentations and imaging findings, making it prone to misdiagnosis and missed diagnosis. This report details the diagnosis and treatment process of a patient with CD complicated by rheumatoid arthritis (RA) who developed chylous leakage postoperatively, highlighting the potential risks of infection and nutritional depletion, aiming to enhance the understanding of CD. PATIENT CONCERNS: A patient with CD complicated by RA developed chylous leakage postoperatively, which posed risks of infection and nutritional depletion. DIAGNOSES: The patient underwent a left axillary lymph node excisional biopsy on November 13, 2019, and was diagnosed with HV-CD based on pathology. INTERVENTIONS: No further axillary lymph node dissection or adjuvant therapy was performed. Postoperatively, the patient developed significant chylous leakage from the biopsy incision, which resolved after 2 weeks of drainage, dietary modifications, and anti-infective treatment. OUTCOMES: Follow-up showed no disease progression, and the chylous leakage resolved with appropriate management. LESSONS: A history of RA may be associated with the onset of CD. HV-CD generally has a favorable prognosis, and chylous leakage post-axillary lymph node biopsy, though rare, can be effectively managed with appropriate drainage, dietary control, and infection prevention.