KNH has turned 106 years and it had its Centenary Celebration in 2001. The Hospital was built to fulfil the role of being a National Referral and Teaching Hospital, as well as to provide medical research environment. Established in 1901 with a bed capacity of 40, KNH became a State Corporation in 1987 with a Board of Management and is at the apex of the referral system in the Health Sector in Kenya.

It covers an area of 45.7 hectares and within the KNH complex are College of Health Sciences (University of Nairobi); the Kenya Medical Training College; Kenya Medical Research Institute and National Laboratory Service (Ministry of Health).

KNH has 50 wards, 22out-patient clinics, 24 theatres (16 specialised) and Accident & Emergency Department. Out of the total bed capacity of 1800, 209 beds are for the Private Wing.

There is a Doctors Plaza consisting of 60 suites for various consultant specialities. The hospital offers a wide range of diagnostic services such as Laboratories, Radiology/Imaging and Endoscopy among other specialised services. Sometime, the average bed occupancy rate goes to 300%. In addition, at any given day the Hospital hosts in its wards between 2500 and 3000 patients. On average the Hospital caters for over 80,000 in-patients and over 500,000 out-patients annually.