Abstract: Context: Measurement programs have been around for several decades but have been often misused or misunderstood by managers and developers. This misunderstanding prevented their adoption despite their many advantages. Objective: In this paper, we present the results of an empirical study on the impact of a measurement program, MQL ("Mise en Qualite` du Logiciel", French for "Quality Software Development"), in an industrial context. Method: We analyzed data collected on 44 industrial systems of different sizes: 22 systems were developed using MQL while the other 22 used ad-hoc approaches to assess and control quality (control group, referred to as "ad-hoc systems"). We studied the impact of MQL on a set of nine variables: six quality factors (maintainability, evolvability, reusability, robustness, testability, and architecture quality), corrective maintenance effort, code complexity, and the presence of comments. Results: Our results show that MQL had a clear positive impact on all the studied indicators. This impact is statistically significant for all the indicators but corrective maintenance effort. Conclusion: We bring concrete evidence that a measurement program can have a significant, positive impact on the quality of software systems if combined with appropriate decision making procedures and corrective actions.