Fatigue crack growth experiments were conducted on surface flaws in a high-strength titanium alloy. Surface crack lengths in the range 50-μm to 8 mm were investigated under both increasing and decreasing ΔK conditions. Crack length and closure loads were determined from load-displacement data obtained with the aid of a laser interferometric displacement gage, which has resolution capability at 0.01 μm. Stress ratios of 0.1, 0.5, and −1.0 and net-section stress levels from 0.2 to 0.9 of yield stress were utilized. The applied stress intensity factor range, ΔK, correlated crack-growth-rate data for R = 0.1 and R = −1, but all R = 0.5 data fell along a separate band. The effective stress intensity factor range ΔKeff determined from closure data, consolidated most of the data into a single band, but some small-crack data fell outside the band. Fracture surface roughness and plasticity were concluded to be the primary features contributing to crack closure.