BACKGROUND Cardiotrophin 1 (CT-1) is an interleukin 6-related cytokine recently implicated in cardiac hypertrophy and vascular damage in essential hypertension (EH). We aimed first to determine CT-1 levels in naive, untreated patients with grade I EH (UH) as compared with normotensive (NT) individuals and, second, to investigate a possible association of CT-1 levels with indices of arterial stiffness. METHODS We enrolled 45 consecutive untreated patients recently diagnosed with grade I EH by means of office and ambulatory blood pressure (BP) measurements and 25 age- and sex-matched NT subjects. CT-1 levels were measured with a commercially available enzyme-linked immunosorbent assay kit, and indices of arterial stiffness were determined by applanation tonometry. RESULTS CT-1 levels were significantly elevated in UH patients compared with NT subjects (P < 0.001). Furthermore, CT-1 levels correlated positively with office, ambulatory and central BP. A significant bivariable correlation was also found between CT-1 levels and pulse wave velocity (P = 0.02). In the multivariable analysis, central systolic and diastolic BP proved the only significant predictors of CT-1 levels after controlling for other related factors. CONCLUSIONS To our knowledge, this is the first study that correlates CT-1 levels with ambulatory and central BP, as well as with pulse wave velocity in patients with essential hypertension. Thus, studying the effects of CT-1 in the cardiovascular system in patients with EH represents a promising area of investigation in the future.