Context: First-generation somatostatin receptor ligands (fg-SRLs) represent the mainstay of medical therapy for acromegaly, but they provide biochemical control of disease in only a subset of patients. Various pretreatment biomarkers might affect biochemical response to fg-SRLs. Objective: To identify clinical predictors of the biochemical response to fg-SRLs monotherapy defined as biochemical response (insulin-like growth factor (IGF)-1 ≤ 1.3 × ULN (upper limit of normal)), partial response (>20% relative IGF-1 reduction without normalization), and nonresponse (≤20% relative IGF-1 reduction), and IGF-1 reduction. Design: Retrospective multicenter study. Setting: Eight participating European centers. Methods: We performed a meta-analysis of participant data from 2 cohorts (Rotterdam and Liège acromegaly survey, 622 out of 3520 patients). Multivariable regression models were used to identify predictors of biochemical response to fg-SRL monotherapy. Results: Lower IGF-1 concentration at baseline (odds ratio (OR) = 0.82, 95% confidence interval (CI) 0.72–0.95 IGF-1 ULN, P = .0073) and lower bodyweight (OR = 0.99, 95% CI 0.98–0.99 kg, P = .038) were associated with biochemical response. Higher IGF-1 concentration at baseline (OR = 1.40, (1.19–1.65) IGF-1 ULN, P ≤ .0001), the presence of type 2 diabetes (oral medication OR = 2.48, (1.43–4.29), P = .0013; insulin therapy OR = 2.65, (1.02–6.70), P = .045), and higher bodyweight (OR = 1.02, (1.01–1.04) kg, P = .0023) were associated with achieving partial response. Younger patients at diagnosis are more likely to achieve nonresponse (OR = 0.96, (0.94–0.99) year, P = .0070). Baseline IGF-1 and growth hormone concentration at diagnosis were associated with absolute IGF-1 reduction (β = 0.90, standard error (SE) = 0.02, P ≤ .0001 and β = 0.002, SE = 0.001, P = .014, respectively). Conclusion: Baseline IGF-1 concentration was the best predictor of biochemical response to fg-SRL, followed by bodyweight, while younger patients were more likely to achieve nonresponse.