While an established protocol exists for diagnosing individuals with the fragile X-associated tremor/ataxia syndrome (FXTAS), a quantitative measure of tremor and ataxia is needed. Using the CATSYS system to quantify movement abnormalities, we were able to record tremor, postural sway, manual (hand and finger) coordination, and reaction time in males with the FMR1 premutation, both with and without FXTAS, and compare them to controls. We evaluated 16 males diagnosed with FXTAS, 16 males with the premutation without FXTAS (non-FXTAS), and 14 age-matched controls. The CATSYS system detected, in the dominant hand, a difference in intention tremor between the FXTAS group and controls (P = 0.0008). The 30-sec postural sway tasks revealed differences between the FXTAS group and controls, both with eyes open and closed (P = 0.0004 and P = 0.0031, respectively). There was also a difference between FXTAS and non-FXTAS 30-sec postural sway performances with eyes open (P = 0.0008). The 10-sec postural sway tasks (with eyes closed) served to confirm the differences between the FXTAS group and both the controls (P = 0.0017) and non-FXTAS premutation carriers (P = 0.0016). These results demonstrate that the quantitative measures of the CATSYS system can document significant differences in intention tremor and postural sway in patients with FXTAS compared to controls.