Differentiating a contact lens-induced peripheral ulcer (CLPU) from early stage microbial keratitis (MK) is primarily based on clinical judgment rather than on microbiologic or histopathologic investigations. For this reason, tests do not provide valuable information at the early stages in the clinical course of MK. Whereas in gross terms, the clinical picture of MK is more acute and severe than CLPU, clinical features of the two can overlap, sometimes resulting in errors of judgment and mismanagement. This article provides clinical clues that help distinguish the two conditions. In addition, a scoring system has been devised for MK and CLPU. Microbial keratitis (MK) is a dreaded complication for contact lens wearers. Although the risk is small, the large population of contact lens (CL) users have made CL wear a major predisposing factor for corneal infection. The reported incidence of MK among CL wearers may be inaccurate because it can be easily confused with its sterile counter part, contact lens-induced peripheral ulcer (CLPU). An accurate initial clinical impression is critical in avoiding mismanagement of these conditions. Clinical differentiation between infected and sterile corneal infiltrates in CL wearers has been addressed in the literature. We suggest a scheme for distinguishing early stage MK from CLPU.