Cancer is a cause of high morbidity and mortality. It is not uncommon for a patient to have more than one primary tumour. This review summarises the knowledge of collision tumours which are defined as two adjacent neoplasms in the same organ, while a collision metastasis is the rare occurrence of two different primary cancers metastasising to the same anatomical site. Identification of collision metastasis is a diagnostic challenge and relies on histopathological examination. As it might have profound impact on prognosis and treatment decisions, it is important to create awareness among both pathologists and clinicians of this phenomenon.