Background US has proven valuable in the diagnosis of subpleural pulmonary lesions (SPLs); however, existing US indicators have limitations. Purpose To propose and validate a revised contrast-enhanced (CE) US indicator for differential diagnosis of benign and malignant SPLs and to compare its performance with existing CE US diagnostic criteria. Materials and Methods This prospective study (Chinese clinical trial registry, ChiCTR1800019828) enrolled patients with SPLs between May 2019 and August 2020. They were divided into a developmental cohort (DC) and a validation cohort (VC). In the DC, the optimal indicator was selected from five CE US indicators. In the VC, the selected indicator was compared with existing CE US diagnostic criteria using the area under the receiver operating characteristic curve (AUC). Pathologic analysis, microbial evidence, and clinical follow-up were used as reference standards for all SPLs. Results A total of 902 participants (DC, 424 participants; VC, 478 participants) with SPLs (mean age, 56 years ± 17; 593 men) were evaluated. The arrival time (AT) difference ratio proved to be the optimal indicator to distinguish benign from malignant SPLs. In the overall (regardless of lesion size), large (vertical diameter >3 cm), and small (vertical diameter ≤3 cm) lesion groups, the cutoff values of the AT difference ratio were 43%, 42%, and 50% and the AUCs obtained from the VC were 0.91 (95% CI: 0.88, 0.93), 0.97 (95% CI: 0.94, 0.98), and 0.77 (95% CI: 0.71, 0.83) respectively, which were higher than those of lesion-lung AT difference greater than 2.5 seconds (0.81 [P < .001], 0.85 [P < .001], and 0.7 [P = .005], respectively), lesion AT greater than 7.5 seconds (0.65 [P < .001], 0.64 [P < .001], and 0.63 [P < .001], respectively), and lesion AT greater than 10 seconds (0.67 [P < .001], 0.68 [P < .001], and 0.64 [P < .001] respectively). Conclusion The US contrast agent arrival time difference ratio enables better differentiation of benign and malignant subpleural lesions when compared with existing diagnostic criteria. Online supplemental material is available for this article. Published under a CC BY 4.0 license.