Cytogenetic analysis of Quercus robur was conducted to investigate any relationship between oak forest decline and cytogenetic abnormalities. Chromosomes of Quercus robur specimens were successfully stained using the double-staining method with Feulgen and Giemsa. The studies revealed that specimens had chromosome complements of 2n=2x=24 or 2n=2x=24+1B. Cytogenetic analyses of mitosis were satisfactory using either root tip or leaf bud meristems. Choromosomal aberrations such as anaphase and telophase bridges, lagging chromosomes and micronuclei were noticed in meristematic cells of seedlings, saplings and mature trees. A relationship between different levels of decline and cytogenetic abnormalities, together with variability of isoperoxidases could not be established. The study indicated that cytogenetic studies are useful for identifying the degree of decline in Quercus robur.