Purpose. To introduce the simplified Therapeutic Intervention Scoring System (TISS-28) and to employ the original Therapeutic Intervention Scoring System (TISS-76) and Simplified Acute Physiological Score (SAPS) version II in critically ill adult patients in order to describe the validity and reliability of TISS-28 as a suitable measure of quantifying nursing workload in the adult intensive care units (ICUs) of a public sector hospital in Johannesburg. Objectives. To describe the profile of patient admissions to the ICUs, to investigate the impact of the patients’ profile on the requirements for nursing workload, and to validate the use of the TISS-28 as a measure for quantifying nursing workload in this setting. Design. A non-experimental, comparative, correlation and prospective two-staged design was utilised to meet the study objectives. Stage I involved face and content validation of TISS-28 by a panel of 6 ICU nurse experts. Stage II involved assessment of concurrent and construct validity as well as inter-rater reliability of TISS-28 using 105 participants drawn from trauma, cardiothoracic and multidisciplinary ICUs. Data necessary for the calculation of TISS-28, TISS-76 and SAPS II were recorded for each patient in the ICU at 24 and 48 hours after admission and in the wards after discharge within 24 - 48 hours. Descriptive and inferential statistics were used to analyse data. Results. A content validity index (CVI) of 0.93 was found for TISS-28. A significant positive correlation was found between TISS-28 and TISS-76 scores (r=0.7857, p=0.0001). Although the correlation between TISS-28 and SAPS II was significant (p=0.0317), it was small (r=0.2098). A significant intra-class correlation (ICC) was found for the data collected from a sample of patients by the researcher and expert assistant researcher (ICC=0.99; p=0.0001). Conclusions. The findings support the validity and reliability of TISS-28 and hence its feasibility for use in South African ICUs. Recommendations for nursing education, practice, management and research are proposed.