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In patients with systemic sclerosis, a ratio between forced vital capacity (FVC) and diffusing capacity of carbon monoxide (DLCO, FCV%/DLCO%) >1.5 might be a predictor of pulmonary hypertension (PH). The aim of this study is, therefore, to evaluate whether this index can be used in patients with PH, regardless of etiology. 83 consecutive outpatients with suspected PH at non-invasive work-up underwent spirometry and DLCO test before right heart catheterization (RHC); FVC%/DLCO% ratio was then calculated and compared with mean pulmonary-artery-pressure (mPAP) and mortality at 5-year follow-up. Significant correlations between FVC%/DLCO% and PAsP and mPAP levels were found (p < 0.05). After ROC curve analysis and definition of best cut-off values for PAsP and FVC%/DLCO%, increased mPAP values at RHC were observed comparing subjects with both PAsP and FVC%/DLCO% values below cut off values (-/-), either PAsP or FVC%/DLCO% above cut off values (±), or both above (+/+) (p < 0.05). Poorer survival rates are observed at follow-up with higher FVC%/DLCO% values (0% for <1, 17.4% for 1-3, 33.3% for >3, p < 0.05), when comparing subjects with either increased PAsP and FVC%/DLCO% values or both with those with lower (log-rank p < 0.05). Even in subjects with mPAP at RHC >25 mmHg, increased FVC%/DLCO% values predicted a worse outcome (p < 0.05). FVC%/DLCO% values are related to mPAP in subjects with suspected PH, and may further stratify the risk of mortality in addition to PAP.