Paediatric Obsessive-Compulsive Disorder (OCD) is associated with significant family accommodation (FA), which frequently results in heightened parental distress, increased OCD severity and impairment. Examining factors which might drive FA is an important focus for the field. This study aimed to examine parents' report of children's emotion regulation (ER) and associations with OCD severity, externalising symptoms, and FA. Participants were 76 youth (7 to 17 years) with a primary diagnosis of OCD and one of their parents. Following child diagnostic and OCD symptom interviews, parents completed study questionnaires. Results indicated that parent-report of children's emotional Lability/Negativity was significantly and positively correlated with child externalising symptoms and FA, whereas children's adaptive ER was significantly and negatively correlated with externalising symptoms only. Furthermore, children's emotional Lability/Negativity predicted externalising symptoms, even when accounting for OCD severity. Lability/Negativity did not predict FA after controlling for OCD severity and externalising symptoms, however it was a significant moderator of the relationship between OCD severity and FA. These findings extend the growing body of literature on ER and OCD in youth and highlight the importance for clinicians to specifically address such deficits in ER as a part of OCD treatment.