BACKGROUND Multiple primary tumors are defined as more than 1 synchronous or metachronous tumor in the same patient. It is important to diagnose each type stage accurately because the treatment is basically directed towards the most advanced and serious primary tumor. CASE REPORT We report a case of advanced mucinous colon cancer and borderline mucinous ovarian tumor that was also implanted with colonic deposits, which presented with acute obstruction. CONCLUSIONS Multiple primary ovarian and colorectal tumors are commonly encountered. In such cases, accurate diagnoses and staging are important. Immunohistochemistry is the most important investigation to differentiate primary cancers in cases of synchronized tumors and metastases.