Wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) were used to study the crystallographic structure of poly-(2-fluorophenylene-2-fluoroterephthalamide) fibres. The unit cell parameters were obtained in WAXD measurements, and AFM yielded complementary information about the conformation of the fluorine-substituted phenylene rings. Results are compared with predicted crystal structures of poly(p-phenyleneterephthalamide) fibres, which were obtained by computer simulation experiments.