Open incision of the patellar tendon (PT) is thought to promote acute vascular responses which ultimately result in an enhanced degree of tendon repair. Such a clinical procedure is commonly applied to patients with refractory tendinitis. The objective of this study was to quantify the vascular adaptations (both anatomical and physiological) to longitudinal incision of the PT, and the resultant effects on tendon organisation. Fifty-four New Zealand White rabbits were separated into 3 experimental groups and 2 control groups. Experimental groups underwent surgical incision of the right PT, and were assessed 3 d, 10 d and 42 d following injury; normal unoperated controls were evaluated at time zero, and sham-operated controls were evaluated at 3 d to control for the effects of incising the overlying skin. Quantitative measures of PT blood supply (blood flow, microvascular volume) and geometric properties of PT substance were obtained for each PT. Histomorphology was assessed to evaluate vascular remodelling and matrix organisation in the healing PT. Longitudinal open incision surgery of the PT led to rapid increases in both blood flow and vascular volume. The incision of overlying tissues alone (sham-operated) contributed to this measurable increase, and accounted for 36% and 42% of the elevated blood flow and vascular volume respectively at the 3 d interval. In the incised PT, blood flow significantly increased by 3 d compared with both time zero and sham-operated controls, and remained significantly elevated at the 10 d interval. Similarly, vascular volume of the incised PT increased at 3 d compared both with time zero and sham-operated controls. At the 10 d interval, the increase in vascular volume was greatest in the central PT substance. By 42 d both blood flow and vascular volume of the incised tendon had diminished, with only blood flow remaining significantly different from controls. In the contralateral limb, a significant neurogenically mediated vasodilation was measured in the contralateral PTs at both early time intervals, but was not seen by the later 42 d interval. With respect to PT geometric properties in the experimental animals, a larger PT results as the tendon matrix and blood vessels remodel. PT cross-sectional area increased rapidly by 3 d to 1·3 times control values, and remained significantly elevated at 42 d postinjury. Morphological assessments demonstrated the disruption of matrix organisation by vascular and soft tissue components associated with the longitudinal incisions. Substantial changes in matrix organisation persisted at 42 d after surgery. These findings suggest that open longitudinal incision of the PT increases the vascular supply to deep tendon early after injury. These changes probably arise through both vasomotor and angiogenic activity in the tissue. Since PT blood flow and vascular volume return towards control levels after 6 wk but structural features remain disorganised, we propose that vascular remodelling is more rapid and complete than matrix remodelling after surgical incision of the PT.