It was 50 years ago when the details of cellular structure were first observed with an electron microscope (EM). Today, transmission electron microscopy (TEM) still provides the highest resolution detail of cellular ultrastructure. The existence of telocytes (TCs) has been described by Hinescu and Popescu in 2005 and up to now, many studies have been done in different tissues. EM has been fundamental in identification and recognition of TC and relationship between TC and stem cells (SCs) in recent years. We present a review on the importance of TEM to provide major advances in the knowledge of the biology of these cells.