BACKGROUND: HMS is characterized by excessive joint mobility, presenting various physical and psychological challenges. Understanding the interplay between these factors is essential for effective HMS management. This study aimed to examine differences in Limits of Stability (LOS) and lumbar proprioception between Hypermobility Syndrome (HMS) and control groups, explore correlations between LOS and proprioception errors, and understand the mediation effects of Kinesiophobia and fatigue on proprioception in HMS individuals. METHODS: In this cross-sectional study, 72 HMS patients and 72 control participants were assessed. LOS was evaluated using a computerized Iso-free stabilometric force platform, lumbar proprioception was measured with digital inclinometers, and Kinesiophobia was quantified using the Tampa Scale of Kinesiophobia (TSK). Fatigue was assessed through standardized fatigue scales. Pearson correlation and mediation analyses were employed for statistical examination. RESULTS: Individuals with HMS showed significantly lower LOS (mean differences ranging from 7.79 to 37.69%) and higher lumbar proprioception errors (mean differences from - 1.09° to -2.88°) compared to the control group. Moderate negative correlations between LOS and proprioception errors were observed (r values from - 0.45 to -0.60). Mediation analysis revealed significant roles of Kinesiophobia (indirect coefficient = -0.14, p = 0.049) and fatigue (indirect coefficient = -0.135, p = 0.047) in the relationship between LOS and proprioception. CONCLUSION: This study highlights significant balance and proprioception deficits in HMS individuals, with substantial mediation effects of psychological and physical factors. These findings emphasize the need for an integrated approach in HMS management, combining physical therapy with psychological interventions.