Background: The aim of the present study was to investigate the incidence of sleep disturbance and insomnia in patients with primary hyperparathyroidism (PHPT), and to evaluate the effect of parathyroidectomy. Methods: A questionnaire was prospectively administered to adult patients with PHPT who underwent curative parathyroidectomy over an 11-month period. The questionnaire, administered preoperatively and 6 months postoperatively, included the Insomnia Severity Index (ISI) and eight additional questions regarding sleep pattern. Total ISI scores range from 0 to 28, with >7 signifying sleep difficulties and scores >14 indicating clinical insomnia. Results: Of 197 eligible patients undergoing parathyroidectomy for PHPT, 115 (58.3 %) completed the preoperative and postoperative questionnaires. The mean age was 60.0 ± 1.2 years and 80.0 % were women. Preoperatively, 72 patients (62.6 %) had sleep difficulties, and 29 patients (25.2 %) met the criteria for clinical insomnia. Clinicopathologic variables were not predictive of clinical insomnia. There was a significant reduction in mean ISI score after parathyroidectomy (10.3 ± 0.6 vs 6.2 ± 0.5, p < 0.0001). Postoperatively, 79 patients (68.7 %) had an improved ISI score. Of the 29 patients with preoperative clinical insomnia, 21 (72.4 %) had resolution after parathyroidectomy. Preoperative insomnia patients had an increase in total hours slept after parathyroidectomy (5.4 ± 0.3 vs 6.1 ± 0.3 h, p = 0.02), whereas both insomnia patients and non-insomnia patients had a decrease in the number of awakenings (3.7 ± 0.4 vs 1.9 ± 0.2 times, p = 0.0001). Conclusions: Sleep disturbances and insomnia are common in patients with PHPT, and the majority of patients will improve after curative parathyroidectomy.