To facilitate the use of the Internal Control Index among UK adults estimates of reliability were calculated among Northern Irish and English samples ( N = 160, N = 108, N = 92). Support was found for the over-all reliability of the scale (a ranging from .86 to .87 for all 3 samples); however, consistent with previous research in the USA, Items 12 and 17 of the scale perform inadequately. Researchers may continue to examine the relationship between these two items and the rest of the Internal Control Index when using the scale in the future to establish the unidimensionality of this measure of locus of control.