The differential diagnosis of a rapidly enlarging neck mass consists of many different benign ((haemorrhagic) cyst) and malignant (anaplastic thyroid cancer (ATC) and lymphoma) causes. ATC is a rare disease with a median survival of 6 months. As early diagnosis and management are key for fast-growing cancers, in our centre we have implemented a dedicated short-stay in-hospital fast-track diagnostic work-up for patients with a rapid growing mass in the neck. The goal of this track is to have a fast diagnostic and therapeutic plan for this disease. Based on three clinical cases we discuss our experience with this fast-track diagnostic work-up for rapidly growing mass in the neck and illustrate the additional value in this clinical entity.