PurposeThe purpose of this research is to examine the effect of internal lean practices on multiple operational performance dimensions, and assess the contingency perspective of these relationships with respect to industry clockspeed.Design/methodology/approachThe study is based on empirical data gathered from 228 manufacturing companies in the Republic of Ireland. The relationships between the constructs are analyzed through regression analysis.FindingsThe results indicate that the relationships between internal lean practices and quality, delivery, flexibility and cost were found to be positive and significant. Further, industry clockspeed was found to moderate the relationship between internal lean practices and quality, delivery and flexibility, but not cost.Practical implicationsWhile internal lean practices can improve operational performance, managers should be aware that internal lean practices are not universally applicable, and the rate of change within an industry should be considered at the time of implementing lean principles.Originality/valueMuch of the lean literature tends to be biased towards its effectiveness. However, empirical evidence shows that not all lean implementation have led to positive results, which has been attributed to the general complexity in the relationship between internal lean practices and performance. We propose to investigate further this relationship by disaggregating operational performance into four of its dimensions, namely quality, delivery, flexibility and cost, and by investigating the possible contingency effect of industry clockspeed.