Aims: The objective of the present study was to verify the correlation of chromosomes 1p and 19q status and expressions of O-6-methylguanine DNA methyltransferase (MGMT), p53 and Ki-67 in diffuse gliomas of World Health Organization grades II and III. Methods: A series of 146 diffuse gliomas, including 45 oligodendrogliomas, 42 oligoastrocytomas and 59 astrocytomas, were analysed by denaturing high-performance liquid chromatography for 1p and 19q status and by immunohistochemistry for MGMT, p53 and Ki-67 expression patterns. The molecular alterations were then correlated with clinicopathological characteristics and with each other. Results: Loss of heterozygosity (LOH) on 1p, combined LOH on 1p and 19q, low MGMT expression and high Ki-67 expression were associated with oligodendroglial tumours, whereas high p53 expression was associated with astrocytic and mixed tumours. LOH on 1p and low MGMT expression were associated with grade II oligodendroglial tumours, whereas high expressions of p53 and Ki-67 were associated with grade III oligodendroglial tumours. In addition, high Ki-67 expression was associated with grade III astrocytomas. LOH on 1p and LOH on 19q were associated with nontemporal oligodendroglial tumours. Nonrandom associations were found between LOH on 1p and LOH on 19q, MGMT expression and p53 expression, and MGMT expression and Ki-67 expression, whereas mutual exclusions were found between LOH on 1p and 19q and p53 expression, and LOH on 1p and Ki-67 expression. Conclusions: The present study revealed significant interrelationships of the investigated molecular alterations and clinicopathological characteristics in diffuse gliomas of World Health Organization grades II and III, which support a promising role of molecular markers in the diagnostic assessment of these neoplasms.