Incomplete or erroneous preoperative evaluation and sarcoma surgeries in which macroscopic or microscopic negative surgical margins cannot be obtained are defined as `unplanned surgery`. Surgical and oncological sequelae resulting from unplanned soft tissue sarcoma surgery may cause different oncological and medicolegal problems, ranging from amputations to life-threatening conditions. In soft tissue sarcomas, the diagnosis and treatment process, including preoperative evaluation, biopsy and surgery, and additional treatments such as chemotherapy and radiotherapy, should be performed by physicians or centers with sufficient knowledge, experience and skills on sarcoma. In cases of unplanned surgery, resection of the tumor bed with wide surgical margins, following local imaging and staging, is the standard treatment. Adjuvant radiotherapy alone has no place in treatment after unplanned surgery and cannot be an alternative to inadequate surgery. In this review, the prevention, results and management of the concept of `unplanned surgery` encountered in treating sarcoma patients are discussed in the light of literature data and our own experience.