A geometrically nonlinear analysis for the extension-twist coupling in pretwisted laminated composite strips in the presence of delamination is developed. Closed-form solutions for strips with internal and edge delaminations are obtained. A parametric study is performed to investigate the influence of delamination length, material system, and stacking sequence on the extension-twist coupling in a class of hygrothermally stable laminates. The model predictions are in good agreement with test data. The results indicate that internal delamination has a negligible influence on the extension-twist coupling behavior while free-edge delamination could result in a significant drop in coupling.