It is generally recognized that there is diversity in the workforce of any enterprise, be it business, government, or civil society. This study therefore seeks to find out the impact of workforce diversity on organizational effectiveness using a Nigerian bank for the study. We used the Blau’s1977 index of heterogeneity to measure the diversity index. While asset growth for the year 2008 and 2009, using 2007 and 2008 as base year was used to measure the growth strategy. To determine group diversity and performance outcomes moderated by workgroup context, a series of hierarchical regression analysis were conducted. The study finds significant correlation between some of the diversity variables as well as individual diversity variables with the measures of organizational effectiveness. Also it reveals that gender and ethnicity are negatively related to both employee productivity and performance bonus. In addition the study find that gender, age and tenure diversities are positively correlated and are significantly related. It is recommended that company executives use good strategies to effectively manage workforce diversity and collaborative research efforts should be done to ascertain the contextual variables that moderate workforce diversity to produce positive performance outcomes.