In recent years, in vivo confocal laser scanning microscopy (CLSM) has become an established method for the non-invasive examination of the skin. In vivo CLSM allows for real-time imaging of micro-anatomic cutaneous structures. It has been used to diagnose ambiguous skin tumors and to measure subclinical tumor spread prior to surgery. By additionally providing high power morphologic information, in vivo CLSM helps to reduce unnecessary biopsies. A multitude of diagnostic features for skin tumors has been published. Here we review published diagnostic in vivo CLSM features, and compare them to our own experience in 100 tumors. In combination with clinical examination and dermatoscopy, in vivo CLSM is a valuable additional tool for non-invasive skin tumor diagnosis.