A study has been made of the striations and fissures developed in the aluminum alloy 2024-T3 during fatigue crack growth. Fissures were found to form on inclined facets. They were uniformly spaced as the result of a shielding process. Striation spacings were in accord with da/dN values at the higher levels of K investigated, but at low K levels striation spacings were larger than the corresponding da/dN values. The percentage of the fracture surface containing striations varied with the K level, ranging from less than 1 % at low K levels to 80 % at higher K levels. The reason for the discrepancy between the spacing of striations and the corresponding da/dN values is discussed.