Factors determining change in ambulatory status were studied over a 12-year observation time in 60 ambulating patients with myelomeningocele. There were 26 female and 34 male subjects with a median age of 22 years (range, 12-54). We used the method of Lindseth to define the neurologic level of the lesion and classified walking ability according to the criteria of Hoffer. The prevalence of spasticity and spine and lower-limb deformities was assessed. Orthopedic and neurosurgical interventions and other medical events were registered, as well as occurrence of pressure sores, musculoskeletal pain, and use of orthoses. There were 19 patients with downward transitions in ambulatory level during the follow-up time. Factors explaining deterioration in these 19 patients included deterioration of the neurologic level of lesion, spasticity, knee and hip flexion contractures, low-back pain, lack of motivation, as well as those of major medical events like stroke, recurrent septicemia, lower limb edema, and invasive surgical interventions.