Background: Improving access to better, more efficient, and rapid cancer diagnosis is a necessary component of a high-quality cancer system. How diagnostic services ought to be organized, structured, and evaluated is less understood and studied. Our objective was to address this gap. Methods: As a quality initiative of Cancer Care Ontario’s Program in Evidence-Based Care, the Diagnostic Assessment Standards Panel, with representation from clinical oncology experts, institutional and clinical administrative leaders, health service researchers, and methodologists, conducted a systematic review and a targeted environmental scan of the unpublished literature. Standards were developed based on expert consensus opinion informed by the identified evidence. Through external review, clinicians and administrators across Ontario were given the opportunity to provide feedback. Results: The body of evidence consists of thirty-five published studies and fifteen unpublished guidance documents. The evidence and consensus opinion consistently favoured an organized, centralized system with multidisciplinary team membership as the optimal approach for the delivery of diagnostic cancer assessment services. Independent external stakeholders agreed (with higher mean values, maximum 5, indicating stronger agreement) that dap standards are needed (mean: 4.6), that standards should be formally approved (mean: 4.3), and importantly, that standards reflect an effective approach that will lead to quality improvements in the cancer system (mean: 4.5) and in patient care (mean: 4.3). Interpretation: Based on the best available evidence, standards for the organization of daps are offered. There is clear need to integrate formal and comprehensive evaluation strategies with the implementation of the standards to advance this field.