The operative treatment of mallet fractures of more than one third of the articular surface is controversial. The purpose of this study was to evaluate the complications and functional outcome of extension block pinning technique. Thirty-six consecutive patients with mallet fractures that involved more than one third of the joint surface were treated by extension block pinning a median of 3 days after injury (range 0-35, mean 7). Clinical outcome was graded according to Crawford's criteria. At a median follow-up of 16.5 months (range 2.5-52, mean 20) 23 patients had an excellent or good result, 11 patients had a fair, and 2 patients a poor, clinical outcome according to Crawford's criteria. None of the patients complained of pain. The median extension loss was 0 degrees (range 0-20, mean 4) and the median flexion was 70 degrees (range 30-95, mean 68). Eight patients had operative or direct postoperative complications including superficial infection (n = 6), loss of Kirschner wire (K-wire) fixation (n = 1), and K-wire mal position (n = 1). The extension block pinning technique is a minimally invasive method of treating mallet fractures with low morbidity and a good functional outcome.