The viability of unicondylar knee arthroplasty (UKA) as a stand-alone or temporising option for the management of gonarthrosis is a topic of considerable contention. Despite recent advances in prosthesis design and surgical technique, as well as mounting evidence of long-term survivorship, UKA remains infrequently used, accounting for just 8-15% of all knee arthroplasties. Instead this group is more typically managed using total knee arthroplasty (TKA). For UKA to warrant increased usage the candidacy for UKA must be prevalent, the outcome must be equivalent or superior to that of TKA, and the costs should be comparatively low. Here we address three issues regarding UKA: 1) a prospective assessment of the proportion of knees needing arthroplasty that are candidates for UKA; 2) retrospective outcome measures comparing TKA, UKA and controls; and 3) an estimation of the difference in costs between TKA and UKA from a hospital perspective. We show in a series of 200 knees that candidacy for UKA is widespread; representing 47.6% of knees. Furthermore, we also show for the first time, that not only is UKA functionally superior to TKA (based on Total Knee Questionnaire (TKQ) scores), but scores in medial and lateral UKA knees do not differ significantly from normal, non-operative age- and sex-matched knees (t=1.14 , p=0.163; and t=1.16 , p=0.255 respectively). Finally, we report that UKA offers a substantial cost saving over TKA ( pound 1761 per knee) indicating that UKA should be considered the primary treatment option for unicompartmental knee arthritis.