Introduction Total hip resurfacing arthroplasty (THRA) is an alternative to conventional total hip replacement (THR) in young patients with osteonecrosis of the femoral head. Series have been small, without criteria regarding extent of necrosis, thus vitiating results. We therefore conducted a retrospective assessment of THRA for small necrosis, to determine (1) implant survival, (2) functional scores, and (3) systemic chromium, cobalt and titanium ion concentrations. Hypothesis The study hypothesis was that the revision rate is low, meeting the National Institute for Health and Care Excellence (NICE) criterion of < 0.5% revision per year. Material and method A single-center single-surgeon retrospective study included 62 patients, for 73 RTHAs, with a mean age of 45.6 years (range: 23–68 years) presenting Ficat stage 3 or 4 osteonecrosis of the femoral head with < 330° total Kerboul angle (frontal + lateral angles) on simple preoperative X-ray. Study data comprised implant survival and preoperative and last follow-up functional scores (Postel–Merle–d’Aubigné, Oxford-12, Harris, and Devane) and titanium, chromium and cobalt blood concentrations. Necrosis size was assessed on preoperative Kerboul angle. Results At a median 8 years’ follow-up (IQR: 5.9–9.3 years), implant survival was 98.6% (95% CI: 97.22–99.98%). Only 1 implant was exchanged, for femoral loosening. Three other patients underwent revision surgery: 2 cases of lavage for infection, and 1 muscle hernia repair. Postel–Merle–d’Aubigné, Oxford-12 and Harris functional scores and Devane activity scores were significantly improved at follow-up, by a median +5 (IQR: 5 to 7), −26 (IQR: −29 to −23), +55 (IQR: 49 to 61) and +1 (IQR: 1 to 2), respectively (all p < 0.001). Ion concentrations at last follow-up for titanium, chromium and cobalt were respectively 4.0 μg/L (range: 3.6–4.1), 1.1 μg/L (range: 0.8–1.9) and 1.1 μg/L (range: 0.6–1.8). Conclusion THRA is a useful option in the long-term for young patients with osteonecrosis with Kerboul angle < 330°. Level of evidence IV, retrospective study.