Presently, there is a global push to extend health insurance to informal workers in developing countries. In Kenya, for instance, the National Health Insurance Fund (NHIF) has taken measures to provide health insurance coverage to informal sector workers through a voluntary contributory scheme. However, the uptake and retention of these workers in the scheme is low. This raises the question: how are institutional mechanisms and processes affecting participation of informal workers in the scheme? Using quantitative survey from two Counties (Nairobi and Kisumu), this paper focusses on providing answers to the question.