Pneumocystis carinii pneumonia is one of these opportunistic infections that are so frequently observed in immunodepressed patients. The usual radiological image is one of interstitial pneumonia. We report the case of a misleading and unusual pseudotumoral form in a female patient with non-Hodgkin malignant lymphoma. The course of the pneumonia was favourable after cotrimoxazole therapy, partial surgical resection and prophylaxis of relapses by inhaled pentamidine.