This study aims to develop and evaluate a Decision-Making Success contingency model to assess its dependency on Internal Control System Quality and Financial Information Quality. The authors developed a study based on a sample of 381 Portuguese managers. The structural equations model was used in the analysis of causal relationships between different constructs. Results show that Internal Control System Quality contributes directly to Decision-Making Success. Moreover, Internal Control System Quality and Financial Information Quality are determining factors for Decision-Making Success since Internal Control System Quality has a significant direct impact on Financial Information Quality (with a 64% coefficient of determination) and indirect on Decision-Making Success. The model justifies 67% of the variance of the dependent variable. This research covers a literature gap, since it identifies innovatively, two independent variables that are determinant for Decision-Making Success from the Portuguese companies' manager perspective. This study is relevant to literature development, as it develops and evaluates an original model, and to managers, in the sense that it identifies factors that contribute to Portuguese companies' success.