Rationale: In interstitial lung disease complicating systemic sclerosis (SSc-ILD), the optimal prognostic use of baseline pulmonary function tests (PFT) and high resolution computed tomography (HRCT) is uncertain. Objectives: To construct a readily applicable prognostic algorithm in SSc-ILD, integrating PFT and HRCT. Methods: The prognostic value of baseline PFT and HRCT variables was quantified in patients with SSc-ILD (n=215) against survival and serial PFT data. Results: Increasingly extensive disease on HRCT was a powerful predictor of mortality (p<0.0005), with an optimal extent threshold of 20%. In patients with HRCT extent 10-30% (termed indeterminate disease), an FVC threshold of 70% was an adequate prognostic substitute. Based upon these observations, SSc-ILD was staged as Limited disease (minimal disease on HRCT or, in indeterminate cases, FVC70%) or Extensive disease (severe disease on HRCT or, in indeterminate cases, FVC<70%). This system (HR=3.46; 95% CI 2.19, 5.46; p<0.0005) was more discriminatory than an HRCT threshold of 20% (HR=2.48; 95% CI 1.57, 3.92; p<0.0005) or an FVC threshold of 70% (HR=2.11; 95% CI 1.34, 3.32; p=0.001). The system was evaluated by four trainees and four practitioners, with minimal and severe disease on HRCT were defined as clearly <20% or clearly >20% respectively, and the use of an FVC threshold of 70% in indeterminate cases. The staging system was predictive of mortality for all scorers, with prognostic separation higher for practitioners (HR= 3.39-3.82) than trainees (HR = 1.87-2.60). Conclusions: An easily applicable Limited/Extensive staging system for SSc-ILD, based on combined evaluation with HRCT and PFT, provides discriminatory prognostic information.