Introduction: Venous convulsion after reconstructive microsurgery procedures is one major complication a surgeon has to deal with. Today, especially in the field of reconstructive microsurgery, medicinal leech therapy enjoys a renaissance. The potential risks such as infections associated with leech therapy are generally underestimated and not sufficiently discussed in literature. Method/patients: We present five male patients with an average age of 47 years. All patients suffered from a trauma incident, which had to be treated as an emergency. Three patients showed, postoperatively, a venous congestion after the reconstructive procedures. Another two patients with flap reconstruction and flap training developed venous problems after 12 and 14 days. In all five cases, the indication was given to use medical leeches (Hirudo medicinalis). In all the patients, a local infection of the injured extremity could be regarded after beginning with the leech treatment. The treatment duration with medical leeches for postoperative venous congestion was an average of 6 days. Results: The reconstructive procedures in all five cases were unfortunately unsuccessful as major local infections were observed. Microbiological analyses showed, in all cases, an infection with Aeromonas hydrophila. Conclusion: We recommend making a considered indication for leech therapy, to diagnose wound infections early and to think about prophylactic antibiotics in patients with leech application.