Appropriate limb length (LL) and femoral offset (OS) after total hip arthroplasty (THA) are crucial for a successful and lasting outcome. However, intraoperative assessment is difficult. Computed navigation is effective but the use of radiation and of invasive bone references is cause of concern. Imageless, pinless navigation systems have been shown to be accurate in experimental studies. However, almost no clinical validation has been performed. We used a minimally-invasive computer-navigated system (MICNS) in conjunction with an imageless measurement technique for implanting 60 consecutive THAs. Head/neck trial components of different size were applied, and the differences in LL and femoral OS measurements were recorded and compared to the implant manufacturer’s specifications, corrected for the anatomical variations of each patient. The imageless MICNS revealed a valid and accurate intra-operative tool for measuring LL and femoral OS in vivo.