The single-molecule dynamics of the membrane probe diIC(18) dispersed in well-controlled lipid environments were studied. Lipid monolayers and bilayers of DPPC, transferred onto a solid substrate using the Langmuir-Blodgett technique, were utilized to systematically control the environment around single diIC(18) molecules. The single-molecule emission trajectories revealed large intensity fluctuations that were strongly coupled to the lipid environment surrounding the probe molecule. For example, as the surface pressure of a DPPC monolayer was increased from the liquid-expanded/liquid-condensed (pi = 5 mN/m) region to the solid condensed (pi = 30 mN/m) region, the characteristic fluorescence fluctuation times increased from approximately 440 ms to over 1 s. For bilayer films, we found characteristic fluctuation times on the order of 2 s, regardless of which side of the bilayer the probe molecule resided. The monolayer and bilayer results are most consistent with a mechanism for intensity fluctuations driven by small twisting motions in the diIC(18) probe molecule that modify its emission properties. Comparison of the measured time scales with results from NMR studies suggest that the observed single-molecule dynamics are associated with director fluctuations arising from collective motions of the lipid tailgroups. These results clearly reveal an environmental dependence in the single-molecule emission trajectories that can provide a new tool for studying membrane microenvironments and dynamics.