DNA studies of the human genome have shown polymorphic variation at thousands of sites, defining an absolute genetic uniqueness for each individual. There are many circumstances in which it may be desirable to diagnose this molecular individuality, as for instance, in criminal investigations or paternity testing. Several techniques can be used for this DNA diagnosis and we can choose among them the one that best suits the specific problem at hand. In this review we describe the main methodologies in current use to investigate human DNA polymorphisms, discussing the best application of each option, as well as their advantages and disadvantages.