We designed the current study to describe the spectrum of disease expression in systemic sclerosis (SSc) in a large cohort and to develop diagnostic criteria for SSc. We assessed patients in the Canadian Scleroderma Research Group Registry by standardized history, physical examination, and laboratory testing. We performed regression tree analysis to determine the sensitivity of various clinical and serologic features for diagnosing SSc. Over 1000 (n = 1048) patients were included: mean age 55 (+/- 12) years, 87% female, 90% white, mean disease duration 11 (+/- 10) years, and 38% with diffuse skin involvement. Common clinical features were Raynaud phenomenon (98%), sclerodactyly (92%), clinically visible mat-like telangiectasias (78%), skin involvement above the fingers (58%), lung fibrosis (35%), pulmonary hypertension (15%), and gastrointestinal tract involvement (mean number of self-reported symptoms, 4 (+/- 3) out of a possible 14). Almost 90% of patients had at least 1 SSc-related autoantibody, including 34% with anti-centromere and 16% with anti-topoisomerase I. The sensitivity of Raynaud and proximal finger skin thickening for the diagnosis of SSc was only 57%. Addition of clinically visible mat-like telangiectasias and SSc-related antibodies improved the sensitivity to 97%. We conclude that important diagnostic clues in patients with SSc include Raynaud phenomenon, skin involvement, clinically visible mat-like telangiectasias, and SSc-related autoantibodies.