To assess two proposed criteria for the transition from pitting to cracking, corrosion fatigue crack nucleation experiments were conducted on open-hole specimens of 2024-T3 (bare) alloy in a 0.5M NaCl solution at room temperature at different loading frequencies, in conjunction with coordinated studies of pitting corrosion and corrosion fatigue crack growth (CFCG). The proposed criteria are: (1) the stress intensity factor ΔK for an equivalent crack (by modeling the pit as a semi-elliptical surface crack) equaled or exceeded the threshold stress intensity factor (ΔKΔth) for CFCG, and (2) the time-based CFCG rate exceeded the pit growth rate. The nucleation of fatigue cracks was found to be associated with large corrosion pits. The size of the crack-nucleating pits was larger at the lower frequencies. This frequency dependence reflects the competition between pitting and CFCG. Validation of the proposed criteria in terms of the experimental data is presented and discussed.