Much like its international counterparts, the Ethiopian architecture, engineering, and construction (AEC) industry grapples with persistent issues regarding contractual construction disagreements (CCDs) among involved parties. Although prior studies have explored the causes of CCDs in the Ethiopian AEC context through literature review and expert interviews, analyzing these causes and their effects based on actual project data has been overlooked. This study aims to fill this research gap by collecting and analyzing the causes and effects of CCDs in the Ethiopian AEC context. To achieve this objective, the study examined 354 heterogeneous sets of cases from archival documents. Among these cases, 246 (69%) involved contractual claims, while the remaining 108 (31%) represented contractual disputes that underwent attempted resolution through a dispute review expert (DRE) approach (18%), litigation (10%), and arbitration (3%). Quantitative data analysis shows that incomplete design, work variation, late payment issued by the client, late site possession, and excess quantity are the top five causes of disagreements observed in claim cases. Similarly, work variation, late site possession, and late payment issued by the client emerged as the primary sources of disagreement in DRE cases. Arbitration cases saw late payment issued by the client, incomplete design and specification, and poor workmanship as causes of disagreement. Litigation cases were primarily due to late payments issued by the client, late work execution, and late payment issued by the contractor to its subcontractor. Overall, late payments issued by the client stood as the primary cause of recurring CCDs in all cases, resulting in more than 70% of time extensions. The identified causes of CCDs also contributed to 10% of delay damage, 8% of additional costs, and 8% of prolongation costs. The practical contribution of this study extends to critical practical implications for key stakeholders in the industry, providing valuable insights into the causes and effects of CCDs in the Ethiopian AEC context.