Abstract: Multiple primary neoplasms (MPNs) refer to the simultaneous or sequential occurrence of two or more histologically distinct primary malignant tumors in the body, which can originate from the same organ, paired organs, different parts of the same system, or different organs of different systems. The occurrence of MPNs is independent of time, with each primary tumor arising from a distinct tissue rather than being due to invasion, recurrence, or metastasis. The incidence of MPNs is relatively low, and the factors and mechanisms involved in their development are not yet fully understood. Clinically, MPNs are typically classified into the synchronous and metachronous MPNs, with a wide and diverse range of locations. One of the greatest challenges in clinical diagnosis of MPNs is to thoroughly exclude the possibility of metastasis from the first primary tumors, and initial accurate clinical staging also presents a significant challenge. Currently, there is no uniform standard for the treatment of MPNs, nor are there any guideline or protocol to follow. Treatment usually requires multidisciplinary team discussion, taking into account both the characteristics of the tumors themselves and the patient′s performance status and preferences, to implement an integrated therapeutic strategy that may include surgery, radiation therapy, chemo-therapy, targeted therapy, immunotherapy, and so on. There is currently no consensus on the prognostic survival outcomes and factors affecting prognosis in patients with MPNs, with significant variability reported in the literatures. It is difficult to conduct prospective clinical studies on MPNs because it is clinically challenging to accurately predict which patients with the first primary tumor will inevitably develop MPNs. Integrated Rehabilitation Committee for Multiple Primary Neoplasms and Unknown Primary Tumors of Chinese Anti‑Cancer Association and Rare Tumor Committee of Shaanxi Anti‑Cancer Association organize experts in relevant fields nationwide to formulate the Chinese Expert Consensus on Diagnosis and Treatment of Multiple Primary Neoplasms (2024 Edition), aiming to provide reference for oncologists in the diagnosis and treatment of MPNs.