This study analyzed whether genotype can be used to predict development of spinal deformity in patients with diastrophic dysplasia (DD). Severity and natural history of scoliosis vary among patients, but the magnitude of the curves is similar among siblings. Plain radiographs were taken of 69 patients aged 16 years or older. The degree of scoliosis was measured according to Cobb's method. Blood samples were collected from patients clinically diagnosed as having DD and the genotype was determined. Fifty-six patients were found to be homozygous for the Finnish founder DTD mutation, DTDST(Fin). Of these 56, 51 (91%) had scoliosis, with an average curve of 43 degrees (range 12 degrees-188 degrees ). The DTDST(Fin)/R279 W genotype was found in nine patients, and of these, eight (89%) had scoliosis, with an average curve of 34 degrees (range 11 degrees-70 degrees ). The DTDST(Fin)/nondetermined genotype was found in four patients. Three (75%) of them had scoliosis, with an average curve of 126 degrees (range 77 degrees-188 degrees ). Statistical analysis found no difference in the prevalence or magnitude of curves between subgroups. The development and severity of the scoliosis cannot, therefore, be predicted from the genotype. It seems possible that scoliosis development is affected by several genes as well as by external factors.