Methods are provided for diagnosing in a subject a condition, such as a carcinoma, sarcoma or leukemia, associated with hypermethylation of genes by isolating the genes from tissue containing as few as 50 to 1000 tumor cells. Using quantitative multiplex methylation specific PCR (QM-MSP), multiple genes can be quantitatively evaluated from samples usually yielding sufficient DNA for analysis of only 1 or 2 genes. DNA sequences isolated from the sample are simultaneously co-amplified in an initial multiplex round of PCR, and the methylation status of individual hypermethylation-prone gene promoter sequences is then determined separately or in multiplex using a real time PCR round that is methylation status-specific. Within genes of the panel, the level of promoter hypermethylation as well as the incidence of promoter hypermethylation can be determined and the level of genes in the panel can be scored cumulatively. The QM-MSP method is adaptable for high throughput automated technology.