Although NF-kappaB has been reported to be constitutively activated in various neoplasms, little information is available about its clinical significance in astrocytomas. In this study, we investigated the association of NF kappa B1/p50 and pI kappa Ba immunohistochemical expression with clinicopathologic features, vascular endothelial growth factor, Cox-2, and microvascular parameters in paraffin-embedded tissue from 82 patients with astrocytomas. pI kappa Ba expression was positively correlated with nuclear (P = .0010) and negatively with cytoplasmic (P = .0008) NF kappa B1/p50 expression. Nuclear NF kappa B1/p50 and pI kappa Ba expression increased with tumor grade (P = .0001 and P < .0001). Nuclear NF kappa B1/p50 was associated with vascular endothelial growth factor (P = .0079), Cox-2 (P = .0500), and total vascular surface area (P = .0430), although the latter was significant only in grades II and III. pI kappa Ba was also positively correlated with microvessel caliber (pI kappa Ba/area; P = .0087). Multivariate analysis selected NF kappa B/p50 expression as an independent prognosticator not only for the entire cohort (P = .0220), but also for grades II and III (P = .0029) and grade IV cases (P = .0310). Our results suggest that nuclear NF kappa B1/p50 expression is dictated by its interaction with I kappa Ba in astrocytomas and is associated with tumor grade and angiogenic factors, denoting the importance of nuclear NF kappa B/p50 expression in patients' prognosis.