Local collateral vessel formation, increased arm circumference, and upper extremity pain are the most frequently used clinical criteria for upper venous system post-thrombotic syndrome (PTS), a potentially serious complication of central venous catheter-related deep venous thrombosis. However, norms for variation of arm circumferences and vessel prominence have not been established for either children or adults. The objective of this study was to define average arm circumference differences and upper body vein prominence in normal children. Healthy children were recruited for the study at both an inner city continuity care clinic and a suburban private practice office. Efforts were made to include age and race/ethnicity distributions similar to the US population. Children with serious medical conditions or history of central venous catheter use were excluded. After permission was obtained from a parent or guardian, bilateral upper arm circumferences were measured, and data were collected regarding hand dominance, race/ethnicity, gender, age, height, weight, and history of chronic or intermittent arm pain. To evaluate the superficial veins, we developed and utilized an objective 5-point scale of chest, upper arm, neck, and shoulder vein prominence. Two hundred fifteen normal children (age 3–18 yrs, median 7 yrs; 53% female; 47% Caucasian, 21% African American, 26% Hispanic, 6% Asian) were evaluated. The mean variation between arm circumferences was 0.4 ± 0.03 cm (mean± SEM, 95% CI 0.35–0.46), and the mean percent difference between arms was 1.93 ± 0.1% (95% CI 1.7%–2.2%). There was no correlation of arm circumference measurements with age, gender, race/ethnicity, handedness, or body mass index. Of the 215 children examined, 47 (22%) had veins that were more than minimally visible (grade ≥ 2), with 54% of those demonstrating asymmetry in vessel prominence. Race/ethnicity did influence vessel prominence (p = 0.02), with an apparent correlation between vessel prominence and skin pigmentation. Twenty-eight percent of Caucasian and 27% of Hispanic children had veins that were more than minimally visible, while only 9% of African American and 7% of Asian children had veins that were more than minimally visible. There was no correlation between vessel prominence and age, gender, handedness, or body mass index. Although a history of arm pain was reported by 29 children (13%), it was rarely validated by parents. Almost all reports of arm pain were easily explained as muscle strain, sprains, broken bones, or “sleeping wrong,” and only 1 child had parentally confirmed pain of unexplained etiology. In conclusion, arm circumference variation, reports of pain, and prominent superficial veins on the chest wall, neck, shoulder, or arm are encountered frequently in normal children. Caution should be used when applying these criteria for a diagnosis of upper venous system PTS in children with prior or current central venous catheters in place. These data should be employed to develop and validate a scale for more objective diagnosis of PTS.