Stab wounds caused by knives and daggers are usually of different appearances. The knife wound has one edge sharp while the second one is blunt. The wound caused by blow of dagger has both edges sharp. The forensic expert must very often decide whether the knife or dagger was used. The aim of this experimental work was to show how a single-edged knife penetrates the skin and causes the wound typical for the double-edged dagger. The fact was verified. The wound typical for dagger can be found if the knife is used only according to the scheme. The forensic expert can say that a one cutting edge knife was used if the one edge of wound is squared and the other one is sharp. If the both of them are sharp, forensic expert must be very careful in his decision.Key words: stab wounds - knife - dagger - forensic expertise.