Carcinoid tumors are a heterogeneous group of neoplasms arising from the diffuse neuroendocrine system. Pulmonary as well as gastrointestinal carcinoids can be separated into those with low malignant and intermediate malignant potential. DNA losses of chromosome arm 11q are commonly seen in pulmonary neuroendocrine tumors. Conflicting results have been published comparing atypical with typical lung carcinoids with respect to imbalances of chromosome 11. In the present study, a DNA microarray with genomic clones mapped to chromosome 11 was created, and array comparative genomic hybridization (CGH) with DNA derived from formalin-fixed, paraffin-embedded tissue was performed. We investigated 4 typical and 12 atypical carcinoids of the lung and, for comparison, 9 gastrointestinal carcinoids and 6 endocrine pancreatic tumors. We have shown that formalin-fixed, paraffin-derived DNA can be successfully used for array CGH. Alterations of 11q were rarely detected not only in typical carcinoids of the lung but also in gastrointestinal carcinoids. Atypical lung carcinoids that comprised extensive DNA losses also presented retained fragments in between these deleted regions. The array CGH data were consistent with the data of a previously published classical CGH study and were additionally confirmed using fluorescence in situ hybridization in the present investigation.