The pivotal BOLT (Basal cell carcinoma Outcomes with LDE225 [sonidegib] Treatment) study established the durable efficacy and manageable toxicity of sonidegib 200 mg once daily (QD) through 42 months in patients with advanced basal cell carcinoma (BCC). This secondary analysis used expression of Glioma-associated oncogene homolog 1 (GLI1) as a biomarker to assess the extent of Hedgehog pathway inhibition by sonidegib in patients with locally advanced BCC (laBCC) and metastatic BCC (mBCC). The study enrolled 230 patients, 79 and 151 receiving sonidegib 200 and 800 mg QD, respectively. At week 17, GLI1 expression was reduced from baseline by a median percentage (95% confidence interval) of 88.7% (54.6%–93.0%) and 97.0% (77.5%–98.9%) for aggressive laBCC, 97.5% (80.3%–98.8%) and 95.0% (80.7%–97.5%) for nonaggressive laBCC, and 99.1% (96.4%–99.6%) and 99.3% (95.9%–99.9%) for mBCC in the 200 and 800 mg groups, respectively. Substantial repression of GLI1 was observed in patient subgroups stratified by age, sex, BCC cytological subtype, Eastern Cooperative Oncology Group performance status, lesion site, baseline number of BCCs, and prior radiotherapy. Results support further studies on the inhibition of Hedgehog pathway genes by sonidegib in patients with laBCC and mBCC.