The case history is presented of a 20 year old man with Pancoast syndrome caused by a high grade B cell lymphoma. (Thorax 1994;49:92-93) were of unequal size, the right being larger than the left. He reported no other neurological symptoms, nor did he admit to shortness of breath, cough, sputum production, or haemoptysis.There was no past medical or family history of significance, and the only medication he was taking was simple analgesia. He smoked about 20 cigarettes per day and occasionally drank alcohol.On examination he had a small, left sided ill defined scalene node. There was no evidence of anaemia, cyanosis, or clubbing, and he was apyrexial. His pulse rate was 80 beats/min, regular and equal in volume in both arms. There was an apparent harsh aortic ejection systolic murmur which radiated to the carotid areas and the back.Examination of his chest revealed decreased expansion of the left hemithorax and decreased air entry in the left lung. There was mild wasting of his left pectoralis musculature. Abdominal examination revealed nothing remarkable.His left pupil was considerably smaller than his right. There was anhydrosis and a partial ptosis on the left side, signs in keeping with Horner's syndrome. There was marked wasting of the interossei, thenar and hypothenar eminences of his left hand, and there was a decrease in power of all muscle groups in this hand (grade 3/5). Light touch and pain sensation were decreased in the C8 and Ti dermatomal distribution in his left hand and arm. The rest of the neurological examination was normal.Full blood count, peripheral film, and blood urea and electrolytes were all normal on presentation. Chest radiography (fig 1) showed only a subtle abnormality, which was only appreciated on a high quality film. An echocardiogram showed no valvular defects or chamber abnormalities to account for the detected systolic murmur.Magnetic resonance imaging (MRI) of the patient's brachial plexus and upper thorax was performed and showed extensive superior mediastinal (fig 2A) and left hilar lymphadenopathy ( fig 2B). There was no evidence of rib destruction on the chest radiograph or on the MRI scan; a bone scan was not performed. A computed tomographic (CT) scan of the brain and cerebrospinal fluid examination showed no abnormality.The patient underwent a left anterior mediastinotomy, as it was felt that an adequate and diagnostically reliable sample of tissue could not be obtained from the small ill defined scalene node found on clinical examination. At operation it was noted that the left lung was adherent to the mediastinum, which was solid with tumour and hilar gland involvement. Biopsies of the tumour and a sample of bone marrow were taken.Histological examination of the samples showed the mass to be a high grade nonHodgkin's B cell lymphoma of centroblastic, pleomorphic subtype. The bone marrow specimen showed no evidence of infiltration by lymphoma or other tumour.