Microsatellite analysis is a frequently used method for detection of chromosomal deletions by loss of heterozygosity studies and for detection of microsatellite instability. For reliable microsatellite analyses, a tumor cell content of at least 80% is required. Therefore, laser microdissection is an important prerequisite for those studies, allowing the contamination-free isolation of morphologically defined pure tumor cell populations. The combination of exact microdissection and subsequent whole-genome amplification by improved primer extension preamplification polymerase chain reaction (I-PEP-PCR) facilitates the analysis of multiple microsatellite loci in small tumor samples. This is especially important for the investigation of malignant tumors with low tumor cellularity. This chapter describes in detail the use of whole genome amplification by I-PEP PCR and microsatellite analysis in laser microdissected specimens of colon and breast cancer.