The prognosis of left circumflex (LC) versus non-LC in-stent restenosis (ISR) ostial lesions following treatment has not been assessed. We aimed to assess this prognosis. Anecdotally, treatment of ostial LC ISR has been associated with high recurrence rates. We performed a retrospective analysis of patients from our institution who underwent coronary intervention of an ostial ISR lesion between 2003 and 2018. The primary endpoint was target lesion revascularization (TLR) and major adverse cardiovascular events (MACE). Overall, 563 patients underwent ostial ISR lesion intervention, 144 for an ostial LC ISR lesion. Compared to patients with ostial ISR in non-LC lesions, patients with ostial LC ISR were older, had higher rates of diabetes mellitus and previous coronary bypass surgery. At 1-year follow-up, TLR-MACE rates were 26.6% in the LC group versus 18.4% in the non-LC group (p = 0.036). The TLR rate was also higher in the LC group compared to the non-LC group (p = 0.0498). Univariate and multivariate analyses demonstrated a higher TLR-MACE rate for LC versus non-LC ostial ISR lesions. In conclusion, our study shows increased event rates after treatment of LC versus non-LC ISR lesions. Further studies should be done to assess the optimal treatment approach for ostial LC ISR.