PURPOSE: Rapid diagnosis is a key issue in modern oncology, for which one-stop breast clinics are a model. We aimed to assess the diagnosis accuracy and procedure costs of a large-scale one-stop breast clinic. PATIENTS AND METHODS: A total of 10,602 individuals with suspect breast lesions attended the Gustave Roussy's regional one-stop breast clinic between 2004 and 2012. The multidisciplinary clinic uses multimodal imaging together with ultrasonography-guided fine needle aspiration for masses and ultrasonography-guided and stereotactic biopsies as needed. Diagnostic accuracy was assessed by comparing one-stop diagnosis to the consolidated diagnosis obtained after surgery or biopsy or long-term monitoring. The medical cost per patient of the care pathway was assessed from patient-level data collected prospectively. RESULTS: Sixty-nine percent of the patients had masses, while 31% had micro-calcifications or other non-mass lesions. In 75% of the cases (87% of masses), an exact diagnosis could be given on the same day. In the base-case analysis (i.e. considering only benign and malignant lesions at one-stop and at consolidated diagnoses), the sensitivity of the one-stop clinic was 98.4%, specificity 99.8%, positive and negative predictive values 99.7% and 99.0%. In the sensitivity analysis (reclassification of suspect, atypical and undetermined lesions), diagnostic sensitivity varied from 90.3% to 98.5% and specificity varied from 94.3% to 99.8%. The mean medical cost per patient of one-stop diagnostic procedure was euro420. CONCLUSIONS: One-stop breast clinic can provide timely and cost-efficient delivery of highly accurate diagnoses and serve as models of care for multiple settings, including rapid screening-linked diagnosis.