Outcome assessment in haemophilia is important to assess results of prophylactic treatment. Recently, the Haemophilia Joint Health Score (HJHS) was developed to assess early joint damage in children with haemophilia. Thus, the aim of this study was to assess reliability and explore validity of the HJHS in teenagers and young adults with haemophilia. Twenty-two patients with haemophilia (mean age 20.4, range 14–30, including 15 severe) were assessed by the HJHS1.0, Haemophilia Activities List (HAL), SF36 and self-evaluation was performed using a Visual Analogue Scale (VAS) scale. A subset of 12 patients were assessed by three physiotherapists to establish interobserver reliability (intraclass correlation coefficient: ICC). Total HJHS1.0 scores were calculated without overall global gait. Validity was explored by the assessment of Pearson's correlation with all outcome parameters and recent Pettersson scores. Overall outcome was good, with median HJHS score of 5.5 of a maximum 144 (range 0–34), median patients' VAS of 96.5 and maximum scores for HAL and SF36 physical functioning for the majority of patients. Pettersson scores were low (median 3.5 of 78, N = 18). Interobserver reliability was good (ICC 0.84), with limits of agreement of ±7.2 points. ICC was unaffected by different score calculation methods. Exploration of validity in 22 patients showed weak correlations of HJHS scores with patients' VAS (0.33) and HAL (−0.40) and strong correlations with SF36-PF (−0.66) and Pettersson scores (0.86). These results suggest that interobserver reliability of the HJHS1.0 in teenagers and young adults with limited joint damage is excellent. Preliminary data on validity were similar or better than those in children.