Sexually transmitted infections (STIs) are a major public health burden globally and especially in developing countries. The relationship between macroeconomic fluctuations and STIs rates has received scant attention in the literature. In this paper we examine the relationship between economic fluctuations and the incidence rates of STIs in Mexico. Mexico offers an exceptional setting because there is a wide range of development across states and the availability of good quality data that covers a lengthy period. We assemble a unique panel of state-level annual data for the 1993-2012 period, for each of the 32 Mexican states. The data include incidence rates by STI type and age group. Economic activity is measured using GDP per capita and explanatory variables are employed to control for the supply of health care and relevant demographic characteristics. We use the human development index for each state to generate three indicator variables that reflect the level of development: top ten, middle twelve, and bottom ten. Our empirical estimation employs the data at the state-year level and includes time and state fixed effects as well as state time trends. The dependent variables in our econometric specifications are the all-ages and age-specific incidence rates of each STI. The real GDP per capital is our control variables of interest. We include interaction terms to reflect the potential for differing effects depending on whether the state in question is in the top, middle, or bottom level of development. Our estimates indicate that there are important differences along a number of dimensions in how economic fluctuations affect STI incidence rates. In terms of economic development, there is generally no relationship in the top states, a procyclical relationship in the middle states, and a mixed relationship in the bottom states. The associations also vary by type of STI, where the trichomoniasis incidence rate is largely countercylical (especially in the bottom states) and the other types (gonorrhea, herpes and syphilis) are generally procyclical. Finally, the largest relationships are mostly found in the 45-64 age group, whereas there is less of a relationship for the oldest age group. Our findings suggest that during economic expansions, public health officials may want to devote additional resources to efforts to reduce risky sexual behaviors in the middle and bottom states. These efforts could include public awareness advertising, greater efforts at STI testing, and attempts at reducing prostitution.