This study examined the influence of informal groups on organizational performance of University of Nigeria Teaching Hospital, Enugu, Enugu state. Having analyzed the distributed 98 questionnaire, descriptive survey approach was adopted and analyzed using regressions with the help of SPSS version 22.0. This study found positive and significant effect of informal welfare group cohesiveness on organizational productivity of University of Nigeria Teaching Hospital, Enugu. Also, there is positive and significant effect of welfare group norms on organizational performance of University of Nigeria Teaching Hospital, Enugu. It concludes that, this study on “Impact of informal groups on organizational performance” is very timely and unequivocally relevant, considering particularly the recent drive in the country to ensure the revitalization of the University of Nigeria Teaching Hospital, Enugu, Enugu state. Based on the findings the study recommends that, informal groups approach should be adopted by University of Nigeria Teaching Hospital as an integral concept within their organizations, particularly as interventionist strategy to improve performance. Also, an effective informal group should be built by applying practical skills/strategies to maximize organizational performance.