Childhood hypertension has classically been recognized as a secondary disease. However, primary hypertension also occurs in children. The aim of this study was to compare clinical features of pediatric patients with elevated blood pressure, which were referred to an outpatient tertiary unit, and to detect variables associated with the identification of primary hypertension. The records of 220 patients with hypertension followed between 1996 and 2006 were analyzed. The variable of interest was primary hypertension. Logistic regression analysis was applied to identify clinical variables that were independently associated with primary hypertension. Of 220 patients, 33 (15%) had primary hypertension, and 187 (85%) exhibited secondary hypertension. No statistically significant differences were detected in gender, race, age at diagnosis, and systolic/diastolic blood pressure levels between both groups. After adjustment, four variables at baseline remained independently associated with primary hypertension: absence of signs/symptoms (OR 18.87, 95% CI 6.32-56.29), normal serum creatinine (OR 0.02, 95% CI 0.00-0.27), family history of hypertension (OR 3.03, 95% CI 1.04-8.79), and elevated body weight (OR 1.06, 95% CI 1.02-1.10). The absence of signs/symptoms, normal serum creatinine, family history of hypertension, and overweight/obesity at admission are clues to diagnose primary hypertension in childhood.