BACKGROUND: The objective of this study is to demonstrate the relationship between the volume of a parathyroid adenoma and the preoperative biochemical parameters in patients undergoing surgery for primary hyperparathyroidism. METHODS: The medical records of 68 patients who underwent a parathyroidectomy for a single parathyroid adenoma were retrospectively reviewed. The volume of the adenoma was estimated using its measured size and a mathematical formula. The correlation between the volume of the parathyroid adenoma and the preoperative laboratory data was assessed. RESULTS: There were no correlations between the estimated volume of the adenoma and the serum calcium, alkaline phosphatase and parathyroid hormone levels. However, the volume of the adenoma was associated with the preoperative level of serum phosphorus. After excluding 5 adenomas with cystic degeneration, a positive correlation was noted between the adenoma volume and the preoperative levels of alkaline phosphatase and parathyroid hormone. CONCLUSION: The preoperative serum levels of calcium, alkaline phosphatase and parathyroid hormone are of limited use to predict the volume of the parathyroid adenoma in patients with a single parathyroid adenoma. We suggest that the absence of a correlation between the volume of the adenoma and the biochemical parameters can be attributed to the cystic degeneration of the adenomas.