We report the case of a non-Hodgkin's lymphoma in an isolated and not previously diagnosed "adult polycystic liver disease". In this case, a rheumatism-like presentation was associated with the discovery of multiple nodular and cystic lesions in the liver. Of these, the former were related to lymphoma involvement, the latter to pre-existent liver disease. The singularity of the case, not previously reported, and some difficulties met in diagnosing the two pathologies, justify the report.