Abnormal DNA methylation can be used as a biomarker in cancer patients. For such purposes, it is important to determine precisely the fraction of methylated molecules in an analyzed sample. A technology we term Methyl-BEAMing achieves this goal. Individual bisulfite-treated DNA molecules can be PCR-amplified within aqueous nanocompartments containing beads, resulting in a population of beads each containing thousands of copies of the template molecule. After hybridization with probes specific for methylated sequences, the beads can be analyzed by flow cytometry. This approach enables detection and enumeration of one methylated molecule in a population of ∼5000 unmethylated molecules. Methyl-BEAMing provides digital quantification of rare methylation events and is generally applicable to the assessment of methylated genes in clinical samples.