The growth of 'small', half-penny shaped surface fatigue cracks in a precipitation hardened aluminum alloy is compared with the growth of 'large' cracks in fracture mechanics type specimens. I t IS found that the small cracks grow much faster than LEFM equivalent large ones, and also experience growth rate perturbations. It is suggested that localixd microplasticity in nominally elastic specimens IS responsible for the rapid growth of small cracks and that grain size limitations on the microplastic regions cause transient dcceleratioiis and sometimes permanent arrest. in crack growth.