“One-Day Diagnosis” (1DD) for hepatobiliary and pancreatic (HBP) diseases is an innovative care pathway that combines, on the same day, surgical consultation, medical imaging, anesthesia, diagnosis announcement, and therapeutic support consultations. The objective was to evaluate the length of the 1DD care pathway compared to a conventional one. The prospective “1DD care pathway” arm included 330 consecutive patients (January 2017–April 2019) vs. 152 (November 2014–November 2015) in the retrospective “conventional” one. In the 1DD group, diagnosis was made on the same day in 83% of consultations vs. 68.4% (p = 0.0005). Although there was no difference in overall time to diagnosis, diagnostic and therapeutic management was faster in the 1DD group (1 day vs. 15 days, p < 0.0004). In addition, 77% of patients who benefited from 1DD were very satisfied with their treatment overall. The mean cost of the 1DD consultation was EUR 176.8 +/− 149 (range: 50–546). The median cost of the overall program was similar (EUR 584 vs. EUR 563, p = 0.67). As an organizational innovation, the 1DD for HBP pathologies is a promising care pathway that optimizes diagnostic and therapeutic management, without creating medical overconsumption or additional costs. Given patient satisfaction, this model should be generalized to optimize cancer care by adapting it to the constraints of different healthcare structures.