Background: An optimal number of health workers, who are appropriately allocated across different occupations and geographical regions, are required to ensure population coverage of health interventions. Health worker shortages in HIV care provision are highest in areas that are worst hit by the HIV epidemic. Kenya is listed among countries that experience health worker shortages (< 2.5 health workers per 1000 population) and have a high HIV burden (HIV prevalence 5.6 with 15.2% in Nyanza province). We set out to determine the optimum number of clinicians required to provide quality consultancy HIV care services at the Jaramogi Oginga Odinga Teaching and Referral Hospital, JOOTRH, HIV Clinic, the premier HIV clinic in Nyanza province with a cumulative client enrolment of PLHIV of over 20,000 persons. Case presentation: The World Health's Organization's Workload Indicators of Staffing Needs (WISN) was used to compute the staffing needs and sufficiency of staffing needs at the JOOTRH HIV clinic in Kisumu, Kenya, between January and December 2011. All people living with HIV (PLHIV) who received HIV care services at the HIV clinic at JOOTRH and all the clinicians attending to them were included in this analysis. The actual staffing was divided by the optimal staff requirement to give ratios of staffing excesses or shortages. A ratio of 1.0 indicated optimal staffing, less than 1.0 indicated suboptimal staffing, and more than 1 indicated supra optimal staffing. The HIV clinic is served by 56 staff of various cadres. Clinicians (doctors and clinical officers) comprise approximately one fifth of this population (n = 12). All clinicians (excluding the clinic manager, who is engaged in administrative duties and supervisory roles that consumes approximately one third of his time) provide full-time consultancy services. To operate at maximum efficiency, the clinic therefore requires 19 clinicians. The clinic therefore operates with only 60% of its staffing requirements. Conclusions: Our assessment revealed a severe shortage of clinicians providing consultation services at the HIV clinic. Human resources managers should oversee the rational planning, training, retention, and management of human resources for health using the WISN which is an objective and reliable means of estimating staffing needs.