Paediatric acute-onset neuropsychiatric syndrome (PANS) is a neurodevelopmental disorder affecting children's performance in a fluctuating manner. This study investigates the relationship between sensory reactivity and occupational performance in children with PANS during exacerbation phases. Understanding these relationships is crucial for developing tailored interventions and managing the condition effectively. This study is part of a larger project in which a two-period bidirectional case-crossover design was employed to assess sensory reactivity and occupational performance in children with PANS. The current study used data from exacerbation phases only. Parents of children aged 4.6 to 13.1years with PANS were recruited globally, and data were collected via online surveys. The Vineland Adaptive Behaviour Scale (VABS) evaluated occupational performance, and the Sensory Processing Measure (SPM) assessed sensory reactivity. Analysis utilised Pearson correlation to determine the relationships between sensory reactivity and occupational performance domains. Data from 60 participants who completed the SPM and 21 who completed the VABS showed moderate to strong negative correlations between the SPM total and several domain scores (vision, hearing, body awareness, balance, and motion) and the VABS Communication and Daily Living Skills scores, indicating that increased sensory reactivity is associated with decreased occupational performance during exacerbations. No significant correlation was found between sensory reactivity and socialisation skills. Findings highlight the significant relationship between sensory reactivity and occupational performance during PANS exacerbations, particularly in communication and daily living skills domains. Further research is needed to examine factors influencing socialisation skills and to assess the effectiveness of sensory interventions in improving occupational performance. Although there was no direct consumer and community involvement, two researchers on our team have family members with PANS. Their personal experiences provided vital insights into the challenges faced by children with PANS, deeply influencing our study's design, focus, and interpretation, ensuring it reflects the realities of those affected. We examined the relationship between children's daily activities and their sensory reactivity during PANS symptom flare-ups. Parents of children aged 4.6 to 13.1 years completed surveys measuring sensory reactivity and their children's performance of daily tasks. Our findings showed that during symptom flare-ups, children experienced significant difficulties with communication and daily living skills. These challenges were directly related to heightened sensory reactivity during flare-ups. This highlights the importance of providing targeted occupational therapy during these times to help children manage their symptoms and improve their daily functioning.