Background: Unicompartmental knee arthroplasty (UKA) is specifically indicated in isolated unicompartmental arthritis with competent ligaments. Recent series of UKA for unicompartmental arthritis have shown good function, persistence of pain relief, and nearly 90% survivorship at 15 years, even in knees that would perhaps not be considered good indications for UKA today. The perioperative morbidity of UKA is less than total knee arthroplasty. We present our series of 19 octogenarians with tricompartment osteoarthritis (predominant medial compartment involvement) treated with UKA as definitive surgery. Materials and Methods: We performed UKA on 29 knees (19 patients) average 83 years (79-94 years) of either sex from Jan 2002 to Dec 2006. All the patients had tricompartment knee osteoarthritis (with predominant medial and some patellofemoral compartment involvement). Results: The results were evaluated using the Knee Society scores and visual analogue score over an average 48-month follow-up (range, 24 to 81 months). Barring one (medial femoral condyle fracture detected on postoperative radiography), all patients achieved promised levels of satisfaction. Discussion: UKA for tricompartment knee arthritis in the young active patient entails risk of dissatisfaction and failure. We present UKA in select ′very elderly′ patients with tricompartment osteoarthritis (with predominant unicompartment involvement).