Tolerance to and efficacy of a fibrin adhesive injected into thyroid cysts after their evacuation by fine needle puncture was investigated in 60 consecutive patients (52 women, 8 men; mean age 50 [18-82] years) with solitary thyroid cysts. The patients were randomly separated into two groups of 30 each. In group A patients the cysts were completely emptied by fine needle puncture under ultrasound control. In group B patients a fibrin adhesive (0.8-1.4 ml) was subsequently injected. 25 of 30 patients in group A had recurring cysts, twelve of which were larger than the original one. There were 13 recurrences in group B (P < 0.005), but only one was of a larger volume. In each group three patients reported a brief period of pain after the evacuation procedure. The described technique has proven to be reliable and well tolerated. Cysts obliterated by fibrin adhesive recurred less frequently and had a smaller volume than those only evacuated by needle puncture.