Opportunistic infections complicating low dose methotrexate therapy are rare, consisting predominantly of Pneumocystis carinii pneumonia. We report a case of invasive pulmonary aspergillosis which developed in a patient being treated for seropositive rheumatoid arthritis with low dose methotrexate (5-7.5 mg weekly) for 8 years. The patient was successfully treated with itraconazole 200 mg daily for 6 months. This case adds to the growing evidence implicating low dose methotrexate with opportunistic infections and should heighten clinical awareness in patients on this treatment.