Clinical, laboratory, and genetic features measured at the onset of rheumatoid arthritis in 100 patients were compared with the severity of radiological changes in the hands and feet and in the cervical spines at a mean of 7.7 years. HLA-Dw4 was associated with more severe (p = 0.009) and HLA-Dw2 with less severe (p = 0.02)radiological changes in the hands and feet but the single strongest correlation with the severity of peripheral erosions was rheumatoid factor (p = less than 0.0001). Although none of the standard clinical or laboratory parameters correlated with severity of cervical spine changes, the presence of HLA-Dw2 and/or HLA B7 cross-reactive group were associated with more severe radiological changes in the cervical spine (p less than 0.02). Discriminant analysis selected certain standard laboratory parameters which in combination provided the most powerful prognostic index of radiological outcome in the hands and feet which was correct in 82 per cent. The addition of HLA data did not improve this figure. Conversely, the combination of the presence of HLA-Dw2, B27, and older age of onset of disease was found to be the most powerful predictor of the development of cervical spine changes and successfully predicted this complication of RA in 73 per cent.