Purpose The most criticism of antegrade humeral nailing is the potentially deleterious effect on the shoulder function, which is caused by the trauma to the M. supraspinatus (SSP) at the nail insertion site. We describe a new technique of all-arthroscopical intramedullary nailing, which preserves the rotator cuff, and compare it with the conventional open procedure. Methods From 11/2009 to 12/2010 82 patients with unstable, displaced proximal humeral fractures were treated surgically. Twenty-one of these patients received an intramedullary nailing. Sixteen of 21 met the inclusion criteria. Based on the surgeon's arthroscopic experience, patients were assigned to the arthroscopic (group I, n = 8) or open group (group II, n = 8). Both groups were compared due to the replacement results, complications, time of surgery and fluoroscopy. Concomitant intraarticular pathologies were assessed (group I). First clinical results after a median follow-up of 13 months (group I) and 14 months (group II) were reported. Results Between group I and II, no signi?cant differences were seen in patients age [77 years (range 45-90 years) vs. 76 years (range 65-92 years)], gender (6 female/2 male vs. 5 female/3 male) and fracture pattern (six 2-/two 3-part fractures vs. five 2-/three 3-part fractures). The reduction was evaluated by the caput-diaphysis-angle, which was median 137° (range 120-147°) in group I and 132° (range 120-158°) in group II (p = 0.959). Postoperatively, group I showed one varus-, group II two varus- and valgus deformities. Median time of surgery was 75 min (range 45-182 min) versus 70 min (range 40-146 min) (p = 0.442), fluoroscopy time 1.5 min (range, 0.6-3.7 min) versus 1.2 min (range 0.3-2.2 min) in group I and II (p = 0.336). Concomitant pathologies like one traumatic bicipital tendon-lesion and three partial lesions of the SSP were observed and treated in group I. Constant Scores and Visual Analogue Scale did not differ significantly between both groups at the time of follow-up. Conclusions All-arthroscopical humeral nailing is possible, preserves the rotator cuff and provides equal replacement and functional results like the open technique. An arthroscopically visualized optimal nail insertion point provides less frequent head deformities. Level of evidence Level III.