Neuropsychological investigations of FMR1 premutation carriers without FXTAS present one domain resulting in contradictory findings, namely that of mathematical skills. One reason for this might be that standard clinical batteries used so far may be inadequate to uncover precise deficits within specific mathematical skills. In fact, these batteries do not clearly distinguish between specific mathematical abilities and are therefore likely to provide only a generic indication of a deficit. Mathematical skills in a group of females with FMR1 premutation were investigated through the use of an extensive, theoretically grounded battery of mathematical tasks, encompassing counting, number comprehension, numerical transcoding, calculation skills and arithmetic principles. Moreover, the mental representation of numbers was assessed by studying the Spatial Numerical Association of Response Codes (SNARC) effect and mental number line (MNL) bisection. The FMR1 premutation group (N = 18) comprised 29-50 years old women of normal intelligence, who were individually matched on age, sex and education to a group of healthy participants (N = 18). Specific yet subtle weaknesses were detected on processes of basic number understanding such as dealing with analogue scales and certain aspects of number transcoding, in the presence of otherwise spared calculation abilities. (Contains 2 tables.)