One of the earliest sub-clinical stages associated with atherosclerosis is endothelial dysfunction (ED), which has been shown to predict future cardiovascular events. Chronic exercise is thought to improve endothelium-dependent vasodilation; however, few studies have evaluated the effects of acute exercise on vascular function (VF). Moreover, studies evaluating ED following an exercise training program lack a standardized time frame in which to measure VF. Although most studies require subjects to abstain from exercise for 24 hours prior to any VF measure, no study to date has assessed VF longer than 24 hours after the cessation of exercise. Additionally, no studies have compared VF responses in obese and non-obese individuals following acute exercise. Purpose: Therefore, the purpose of this study was to evaluate VF, as determined by the assessment of forearm blood flow (FBF) and vascular reactivity (VR) before and up to 48 hours after a single bout of maximal exercise in obese and non-obese males. Methods: Twelve obese (37.0 ± 1.1 kg/m2) and twelve non-obese (21.9 ± 0.3 kg/m2) males volunteered to participate. FBF was assessed before and during reactive hyperemia (RH). FBF measures were obtained prior to (PRE-E), immediately after (POST-E), and at 1 (POST-1), 2 (POST-2), 24 (POST-24), and 48 (POST-48) hours after exercise. Total excess flow, calculated as the difference between baseline FBF and FBF during RH, was used as an indicator of VR. Blood samples were also obtained at each time point to evaluate the response of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α), which are potential modifiers of VF. Results: Baseline FBF and FBF during RH were significantly (P < 0.05) increased in both groups POST-E before returning to baseline values by POST-1. VR was enhanced in both groups POST-E, although the magnitude of change was greater in non-obese males. VR was significantly (P < 0.05) increased in non-obese males POST-E and was not significantly (P < 0.05) reduced until POST-48. Concentrations of IL-6 and TNF-α were unchanged in response to exercise in non-obese and obese males. Conclusions: An acute bout of maximal exercise significantly increased forearm endothelium-dependent vasodilation in non-obese and obese males. Additionally, an increased reactive vasodilation was observed only in non-obese males following exercise. These results also suggest that in non-obese males, measurements used to verify improvements in VF following exercise training should be employed after a minimum of 48 hours following physical activity.