© 2014 Royal Australian and New Zealand College of Ophthalmologists. To prospectively investigate the safety, tolerability and 24-h intraocular pressure (IOP) patterns in patients with thyroid eye disease (TED) using a contact lens sensor (CLS). Design: Prospective study. Participants: Ten patients with established TED. Methods: Ten eyes of 10 patients were prospectively evaluated in an ambulatory 24-h IOP monitoring session using the CLS (Sensimed AG, Lausanne, Switzerland). Patients pursued daily activities, and sleep behaviour was uncontrolled. Main Outcome Measures: Incidence of adverse events (AEs) and tolerability (scale of 0-10, increasing intolerance) were assessed. IOP patterns were evaluated using a cosinor rhythmometry model, and linear regression slopes were constructed for the transition from wake/sitting (W/S) to sleep/supine (S/S) and vice versa. Results: Mean age was 61.8±21.6 years, and 90% of patients were female. Main AEs were blurred vision (50%), conjunctival hyperaemia (100%) and superficial punctate keratitis (20%). Tolerability of the lens was found to be 1.5±0.7. Positive linear slopes of the CLS signal from wake to sleep were detected (18.0±43.8arbitrary units [a.u.]; P=0.254), whereas at the transition from S/S to W/S a significant decrease (-62.9±56.8a.u.; P=0.010) was found. Five patients (50%) had a significant nocturnal/sleep acrophase with the peak occurring at 6:30 a.m. The mean amplitude of the 24-h curves was 102.2±52.6a.u. Conclusions: In patients with TED, the CLS provides a safe and well-tolerated approach to 24-h IOP monitoring. After modelling the 24-h IOP curves, TED patients were found to have a morning acrophase.