Rab GTPases recruit peripheral membrane proteins and can define organelle identity. Rab18 localizes to the ER but also to the surfaces of lipid droplets (LDs), where it has been implicated in effector protein recruitment and in defining LD identity. Here, we studied Rab18 localization and function in SUM159 cells. Rab18 localized to the ER and to LD membranes upon LD induction, with the latter depending on the Rab18 activation state. In cells lacking Rab18, LDs were modestly reduced in size and numbers, but we found little evidence for Rab18 function in LD formation, LD turnover upon cell starvation, or the targeting of several proteins to LDs. We conclude that Rab18 is not a general, necessary component of the protein machinery involved in LD biogenesis or turnover, but instead likely plays a specialized role in specific cell types