Surplus lines insurers play a crucial role in the marketplace. These companies commonly provided coverage for high capacity, distressed or unique risks, as well as new or emerging risks for which coverage is not available in the admitted market. Though surplus lines insurers play a valuable role in the marketplace and business written by these insurers have grown over time, there has been little academic literature that focuses on this segment of the industry. In this study, we examine whether surplus lines activity differs across regulatory environments, where activity is measured by surplus lines premiums, the number of active surplus lines companies and the concentration of the surplus lines market within each state. We find a positive correlation between premiums written and several regulatory measures, such as greater capital and surplus requirements, higher premium taxes and the existence of state surplus lines associations. The positive correlation with capital and surplus requirements and surplus lines associations is also observed when examining the proportion of surplus lines insurers in states. Finally, we find strong correlations between the concentration of the surplus lines market in states and all regulatory measures considered.