Sciatic nerve tumour was diagnosed in a Staffordshire Bull Terrier cross-bred and a Bichon Frise, both presenting with chronic left hind limb lameness. Neurological examination in each case was consistent with left sciatic nerve deficits and this was confirmed by EMG studies. Rectal examination of both dogs revealed a palpable intrapelvic mass that was not apparent on survey radiographs. A sciatic nerve tumour was identified using MRI in each case. Histological examination of tissue taken from the Staffordshire Bull Terrier cross-bred was consistent with a malignant peripheral nerve sheath tumour.