The application of NMR methods to the non-destructive testing of thermoplastic composites is discussed. NMR imaging of the polymer matrix is restricted to the detection of defects in excess of 5 mm using standard instrumentation. Higher resolution can be achieved by imaging the matrix at high temperatures or by more sophisticated NMR procedures with the practical limit of 0.1 mm or so at present. Composites subject to high fluid exposure during their working life can be examined by NMR imaging of fluid absorbed by the composite which tends to collect in the defect, as illustrated by water in a canine APC2 hip joint. Polymer morphology can be studied using NMR relaxation times but the localised measurement of these features is hindered by the sensitivity of the pulse sequences to inhomogeneities in the radiofrequency across the field of view.