Fifteen patients with partial sacral agenesis were treated over a mean period of 68 months. Partial unilateral agenesis was present in 7 and bilateral sacral agenesis was present in 8. Three important diagnostic features are emphasised: symptoms referable to neurogenic bladder without an obvious neurogenic lesion (all 15 patients); skin or hair abnormalities in the lumbosacral region (9/15) and paraesthesia or other neurological disorders of the lower extremities (8/15). The definitive diagnosis can be made by careful inspection of a plain film of the lumbosacrum. Detrusor contractility was absent in 13 patients but preserved in 2; 11 patients were managed by clean intermittent catheterisation, 2 voided using detrusor contractility and 2 voided by means of the Valsalva/Credé manoeuvre. In 5 patients surgery in the intradural space preserved sexual function and prevented further deterioration in function of the lower extremities but could not restore bladder function that had already deteriorated. Complete continence was achieved in 11 patients and socially acceptable continence in 4. Early diagnosis and conservative treatment with clean intermittent catheterisation are extremely important in management. Should functional deterioration of the bladder and/or sensomotor function of the lower limbs occur, neurosurgery should be performed promptly.