In the course of a screening of fungal extracts for new metabolites with cytotoxic activities cylindrocyclin A (1) was isolated. The producing strain was identified as Cylindrocarpon sp. by microscopy and ITS rDNA sequence analysis. 1 is a novel compound that exhibits cytotoxic acticity against six different cell lines with IC50 values ranging from 11 to 53 microM. 1 has no antibacterial or antifungal activity. The compound is a cyclic nonapeptide comprising three alanines, five leucines and one isoleucine. Four amino acids are N-methylated. Its structure was elucidated by spectroscopic methods.