Background : The determinants of intubation and the response to therapy in COPD patients with hypercapnic respiratory failure were retrospectively reviewed. Methods : This study involved a review of 132 episodes of hypercapnic respiratory failure($PaCO_2;{geq};50;mmHg$ and $pH;{leq};7.35$). The time frame for resolution or the time to intubation of patients who were admitted between 1996 and 1999 was analyzed. Results : Out of 132 hypercapnic episodes, 49(37%) required intubation. A comparison was made with the 83 cases that responded to treatment. Patients requiring intubation had a greater severity of illness, which included a higher APACHE II (Acute Physiology and Chronic Health Evaluation II) score ($20{pm}5$ vs $14{pm}4$ ; p<0.01), a higher WBC, a higher serum BUN, and greater acidosis (pH, $7.23{pm}0.11$ vs $7.32{pm}0.04$ ; p<0.01). Those with the most severe acidosis(pH<7.20) had the highest intubation rate(87%) and shortest time to intubation($2{pm}3;h$). Conversely, those with an initial pH 7.31 to 7.35 were less likely to be intubated(20%), and had a longer time to intubation($97{pm}121;h$). The patients with a pH 7.21 to 7.25($4.1{pm}2.9$ day) required longer period of time to respond to medical treatment than patients with a pH of 7.31 to 7.35($2.2{pm}3.1$ day). Of those patients requiring intubation, half(55%) were intubated within 8 h of admission, and most (75%) within 24 h. Of those patients responding to treatment medical therapy, half(52%) recovered within 24 h and most (78%) recovered within 48 h. Conclusion: Respiratory acidosis at the initial presentation is associated with an increased likelihood of intubation. This should assist in deciding help with the decision whether to treat patients medically, institute noninvasive ventilation, or proceed to intubation.