During a 12 month period of operation of a 0.3 Tesla MRI iron cored resistive scanner 74 cases of syringomyelia were diagnosed on clinical, radiological and/or surgical grounds. Without knowledge of any clinical or radiological data the syrinxes were classified into five groups--idiopathic, idiopathic associated with Chiari malformation, tumour associated, post-traumatic and arachnoiditis associated--and the lesion characteristics within each group were compared. Although MRI was extremely sensitive in picking up even small syrinxes, there was considerable overlap of MRI characteristics across the sub-groups, so that two post-traumatic syrinxes had lesion characteristics identifiable with those of tumour syrinx and one intramedullary tumour syrinx had the MRI characteristics of a benign, idiopathic syrinx. It is concluded that meticulous attention to technique, including axial as well as sagittal T1 weighted sequences, and the administration of intravenous paramagnetic contrast media are necessary for detection and accurate classification of syrinxes.