Aggregation of uncoated ZnS nanoparticles was determined to have an unexpected impact on the particle's photoluminescent properties. Aggregation had significant consequences to both band-edge and trap-site photoluminescence, increasing the former and decreasing the latter. The onset of changes to photoluminescence was influenced by aggregation rate. Results suggest that aggregate structure plays an important role in determining the extent to which changes to photoluminescence occur. Strong evidence is presented in support of the hypothesis that aggregation-induced changes to surface tension are responsible for the observed photoluminescence behavior. We show that changes in photoluminescence can be used to predict the attachment coefficient, in lieu of dynamic light scattering. Additionally, our data indicate that the particle size distribution of aggregating ZnS nanoparticles is invariant across electrolyte concentrations, at a given standard deviation away from the maximum rate of photoluminescence change.