Introduction Pancoast tumour although well described, can still present a diagnostic challenge. The difficulty is that those who develop this type of lung cancer do not have pulmonary symptoms, and even if a chest X-ray is requested, it may appear normal due to the “blind” spot. Here I describe three challenging cases of Pancoast tumour. Two out of the three patients could have been diagnosed earlier, if only the possibility of Pancoast tumour had been considered. I will describe the symptoms, the signs and the neurophysiological findings of the patients in detail. Methods Three cases described. The patients had focused neurological assessment after history taking, followed by EMG and NCS. Case 1: 71 years old female during her angiogram for coronary artery disease experienced strong pain in the top of her right chest. Since then she developed progressive weakness in the right hand along with some numbness and paraesthesia. The patient only had a little discomfort in her neck and shoulder. She was thought to have had a complication during her angiogram and was investigated for that matter. Her chest X-ray was taken and was reported as normal. Case 2: 64 years old male was referred to Neurophysiology with 18-month history of pain in the neck and shoulder and wasted muscles in the hand. Preliminary diagnosis was cervical radiculopathy. On examination the patient was in severe pain and had wasted muscles in the hand. Case 3: 52 years old female presented to Neurophysiology with diagnosis of possible Carpal tunnel syndrome. She had paraesthesia in her hand. The interesting thing regarding this patient was that she had neither weakness, nor wasting. Results All patients had a history of smoking and Horner Syndrome. The NCS and EMG showed abnormalities indicating the lesion of the low trunk of the brachial plexus. One patient had lesion confined to only T1; not recordable medial cutaneous antebrachii sensory response and slightly low median motor response in the symptomatic side. The needle EMG showed evidence of denervation in T1 myotome. The other two had C8 andT1 involved. The NCS and EMG data will be enclosed. In all patients, CT of the thorax ultimately confirmed the diagnosis of Pancoast tumour. Conclusion A certain approach is required in order to diagnose a Pancoast tumour as early as possible. An earlier Neurophisiological examination is helpful in localising the lesion to the low trunk of the brachial plexus. I emphasise the importance of looking for pupils’ asymmetry in every patient with unexplained wasted intrinsic muscles in the hand associated with some sensory symptoms. Even partial Horner Syndrome, such as asymmetric pupils with the symptoms and signs of low brachial plexus in someone with a history of smoking would be highly suggestive of Pancoast tumour. Those patients would warrant prompt CT scan, as chest X-rays can sometimes be unreliable.