Background: A novel oral octreotide formulation was tested for efficacy and safety in a phase III, multicenter, open-label, dose-titration, baseline-controlled study in patients with acromegaly. Methods: We enrolled 155 complete or partially controlled patients (IGF-1 <1.3 x upper limit of normal [ULN], and 2-h integrated GH <2.5 ng/mL) receiving injectable somatostatin receptor ligand (SRL) for >= 3 months. Subjects were switched to 40 mg/d oral octreotide capsules (OOCs), and the dose escalated to 60 and then up to 80 mg/d to control IGF-1. Subsequent fixed doses were maintained for a 7-month core treatment, followed by a voluntary 6-month extension. Results: Of151evaluable subjects initiatingOOCs, 65% maintained responseandachieved the primary endpoint of IGF-1 <1.3 x ULN and mean integrated GH <2.5 ng/mL at the end of the core treatment period and 62% at the end of treatment (up to 13 mo). The effect was durable, and 85% of subjects initially controlled on OOCs maintained this response up to 13 months. When controlled on OOCs, GH levels were reduced compared to baseline, and acromegaly-related symptoms improved. Of 102 subjects completing the core treatment, 86% elected to enroll in the 6-month extension. Twenty-six subjectswhowereconsideredtreatmentfailures (IGF-1 >= 1.3 x ULN) terminatedearly, and23withdrew for adverse events, consistent with those known for octreotide or disease related. Conclusions: OOC, an oral therapeutic peptide, achieves efficacy in controlling IGF-1 and GH after switching from injectable SRLs for up to 13 months, with a safety profile consistent with approved SRLs. OOC appears to be effective and safe as an acromegaly monotherapy.