A 38-year-old male patient who had been treated for Crohn's disease was found to have serum lipase activity that was persistently increased - 10-fold above the normal upper limit. He was diagnosed with chronic pancreatitis based on slightly elevated elastase-1 level and retrograde pancreatography showing slight dilatation of the main pancreatic duct. Therefore, the hyperlipasemia was thought to be due to pancreatitis. However, the serum amylase and trypsin was not increased at any time, and no serious findings suggestive of pancreatitis were detected on morphologic examination. Thus, there were discrepancies between the serum lipase activity and other laboratory and clinical findings. Exclusion chromatography of the patient's serum suggested macromolecular lipase, and further immunologic testing including affinity chromatography, enzyme-linked immunosorbent assay, and immunoprecipitation assay showed that serum lipase was bound to immunoglobulin GK. Therefore, the hyperlipasemia was caused by immunoglobulin-linked lipase, termed “macrolipasemia”. Macrolipasemia has rarely been reported, and this is the first reported case of macrolipasemia accompanied by Crohn's disease.