In this study, we compared the sensitivity and specificity of visual versus quantitative evaluation of skeletal muscle ultrasound in children suspected of having a neuromuscular disorder (NMD). Ultrasonography (US) scans of four muscles (biceps brachii, forearm flexors, quadriceps femoris, anterior tibial muscle) were made in 76 children. All images were visually evaluated using the Heckmatt criteria and quantitatively evaluated with computer-assisted grey-scale analysis of muscle echo intensity. Visual evaluation could achieve a sensitivity up to 71%, with a specificity of 92%. With quantification, a sensitivity of 87% accompanied by a specificity of 67% was found, but other diagnostic values could be achieved, depending on the cut-off point. Quantification resulted in a higher interobserver agreement (kappa 0.86) compared with visual evaluation (kappa 0.53). We conclude that quantification of echo intensity is a more objective and accurate method. Because it can achieve higher sensitivities, it is better-suited for the screening task in the diagnostic phase of children with a NMD.