The purpose of this study was to determine if there is a relationship between ultrasound measured gap size and functional outcomes in non-operatively treated achilles tendon ruptures. Patients who presented with complete achilles tendon ruptures were prospectively randomised to operative or non-operative treatment groups and followed over a one year period. The non-operative patients were selected and reassessed at three months, six months and one year. Patients were included if seen within seven days of their injury and had ultrasound confirmation of a complete tear. Non-operative treatment consisted of a functional bracing protocol with an aircast boot. Ultrasound measures included tear location and gap size in neutral, dorsiflexion, and plantar flexion of the ankle. Outcome measures were re-rupture rates, complications, range of motion, calf circumference, strength, and functional outcome scores. Twenty-five patients were included with complete data. The mean plantar flexion gap was 5.6(+/−7.5mm). The mean dorsiflexion gap was 13.7(+/−12.5mm). Proximal tears were found in 41% of patients, midsubstance in 27%, and distal tears in 32%. At one year follow-up 71% of patients had excellent results with the remaining 29% showing good results. Isokinetic strength, range of motion, and calf circumference measurements were all greater than 90% relative to the contralateral extremity. There were two reruptures and no other complications present. There were no significant relationships between plantar or dorsiflexion gap size and functional outcomes scores or tear location. Gap size was not significantly related to functional outcomes. Non-operative treatment produced very good results at one year follow-up with low complication rates. These results suggest that ultrasound estimation of gap size and location may be of limited clinical value in the management of achilles tendon ruptures.