Neuronal Ceroid Lipofuscinosis type 2 (CLN2) disease is a rare, autosomal recessive disorder typically manifesting in late-infantile children. The disease results in progressive language loss, movement disorders, pain, dementia, vision loss and ultimately death at 8–12 years of age. The 0–6 point Motor-Language CLN2 Clinical Rating Scale was the primary endpoint in the pivotal cerliponase alfa trial for the treatment of CLN2 disease. This analysis aimed to concurrently validate this disease-specific functional rating scale by examining its relationship to the Paediatric Quality of Life Inventory (PedsQL) tool, for which a minimal clinically important difference of 4.5 has been established.1 Data from the phase 1/2 single-arm trial of 23 CLN2 patients treated with cerliponase alfa for a minimum of 97 weeks were used in this analysis (NCT01907087). To determine the relationship between the clinician-reported CLN2 Clinical Rating Scale total score and the proxy-reported PedsQL score at both the total and domain level, simple linear regression followed by mixed effects analyses (to account for within-subject correlation) were conducted. For the simple and mixed effects analyses, there was very strong evidence of a positive correlation between the PedsQL total score and the CLN2 Clinical Rating Scale total score (p<0.001; simple regression adjusted R-squared=0.27; mixed effects CLN2 Clinical Rating Scale parameter estimate [95% confidence interval (CI)]: 5.06 [2.66, 7.44]). It appears this relationship was primarily driven by the PedsQL Physical domain (p<0.001; simple regression adjusted R-squared=0.42; mixed effects CLN2 Clinical Rating Scale parameter estimate [95% CI]: 10.41 [7.21, 13.54]). These results provide evidence of concurrent validity between the CLN2 Clinical Rating Scale and PedsQL score, in particular, with respect to physical function. This relationship suggests a 1-point change on the CLN2 Clinical Rating Scale may be meaningful to patients.