A cystic neck mass can be either malignant or benign; 22% of patients (4/18) admitted with the tentative diagnosis of branchial cyst in a recent 2-year period (1977-1979) had metastatic carcinoma: epidermoid, thyroid or salivary gland. Preoperative fine needle aspiration was diagnostic in 1 instance and unhelpful in 2. Frozen section analysis of the gross specimen invariably provided the correct diagnosis. All patients with malignancies had subclinical primary disease and in 1 instance random biopsies identified its origin. The prudent surgeon will avoid untoward results if he approaches a neck cyst in an adult as if it were malignant. Guidelines he can follow to prevent the inadvertent removal of a metastasis under the misapprehension that it is a benign neck cyst include: 1. Prior to operation, perform a thorough head and neck examination to identify a primary carcinoma; 2. Do a fine needle aspiration of the mass for cytology. A negative report must be considered inconclusive; 3. Make a gross examination in the operating room of the opened cyst and frozen section processing of suspicious areas; 4. Follow with a panendoscopy and random biopsies of appropriate areas and complete the neck dissection on the involved side, after a metastatic deposit has been recognized. The preoperative procurement of contingency consent for these procedures is understood.