Background: Restrictive allograft syndrome (RAS) after lung transplantation (LTx) is associated with the poorer graft survival in patients with chronic lung allograft dysfunction (CLAD). Nevertheless, its diagnostic criteria have not been clearly defined after single-LTx (SLTx). Hence, we studied an SLTx cohort with CLAD to investigate the utility of both computed tomography (CT)-score/volume measures and functional spirometric criteria for the early identification of RAS in this population. Methods: We included 51 patients with SLTx (17 RAS, 17 bronchiolitis obliterans syndrome [BOS], and 17 stable condition). The criteria for RAS diagnosis in SLTx included forced vital capacity (FVC) <80% baseline (BL) or forced expiratory volume in 1 second (FEV1) <80% BL with an FEV1/FVC ratiounchanged or >0.7 and persistent CT-scan-lung opacities. We defined 4 time points (T): T-baseline, T-onset (first CT-scan-opacities), T-follow-up, and T-last. Results: In patients with RAS, the spirometric criteria for RAS at T-onset were reached in only 47% (FVC decline <80% BL [(29%] or FEV1 <80% BL/ratiounchanged or >0.7 [41%]), whereas at the same T-onset date, the graft CT-score increased to 5 (4-6) vs 1 (0-2) at baseline (p < 0.001) (CT - score ≥2 at T-onset in 100% and ΔCT - score ≥2 in 74% of patients with RAS), and the median CT-scan graft volume decreased to 1,722 ml (vs 1,796 ml at T-baseline, p = 0.003) (decreased CT-graft - volume <90% BL in 50% of patients). In contrast, in patients with BOS, CT-score/volume were unchanged at T-onset vs T-baseline (p = 0.8, p = 0.68, respectively). Conclusion: Our results suggest that the use of a simple CT-score and to a lesser extent, CT-volume measures, might allow for the early identification and/or prediction of RAS in SLTx rather than functional criteria.