Background: It is unclear if isolated postoperative cardiac-troponin elevation, often referred to as myocardial injury, represents a pathological event, as control studies in otherwise healthy adults are lacking. Methods: In this single-centre prospective observational cohort study, serial high-sensitivity cardiac troponin T (hscTnT) plasma concentrations were obtained from young, healthy adults undergoing elective orthopaedic surgery at three time points: before operation, 2–6 h, and 18–30 h after surgery. End points were hscTnT increases after surgery: ≥20% (exceeding analytical variability), ≥50% (exceeding short-term biological variability), and ≥85% (exceeding long-term biological variability). The secondary end point was myocardial injury, defined as new postoperative hscTnT elevation >99th % upper reference limit (URL) (women >10 ng litre−1; men >15 ng litre−1). Results: Amongst the study population (n=95), no hscTnT increase ≥20% was detected in 68 patients (73%). A hscTnT increase between 20% and 49% was observed in 17 patients (18%), 50–84% in seven patients (7%), and ≥85% in three patients (3%). Twenty patients (21%) had an absolute ΔhscTnT between 0 and 2 ng litre−1, 12 patients (13%) between 2 and 4 ng litre−1, three patients between 4 and 6 ng litre−1, and one patient (1%) between 6 and 8 ng litre−1. Myocardial injury (new hscTnT elevation >99th%) was diagnosed in one patient (1%). The median hscTnT concentrations did not increase after operation, and were 4 (3.9–5, inter-quartile range) ng litre−1 at baseline, 4 (3.9–5) ng litre−1 at 2–6 h after surgery, and 4 (3.9–5) ng litre−1 on postoperative day 1. Conclusions: One in four young adult patients without known cardiovascular disease developed a postoperative hscTnT increase, but without exceeding the 99th% URL and without evidence of myocardial ischaemia. These results may have important ramifications for the concept of postoperative myocardial injury, as they suggest that, in some patients, postoperative cardiac-troponin increases may be the result of a normal physiological process in the surgical setting. Clinical trial registration: NCT 02394288.