High yield stability and adaptability of storage root are highly desirable attributes of cassava clones. The objective of this study was therefore to evaluate the effect of the genotype x environment interaction (G x E) and the stability of cassava clones developed at IAC. A subset of eight cassava genotypes was chosen in trials of storage root yield, arranged in a randomized complete block design with four replications, in two counties (Araruna and Maringa), in the northwestern region of Parana State, over five growing seasons (1997-2001). The G x E interaction was evaluated by joint variance analysis and stability and adaptability by AMMI analysis. The G x E interaction was significant (P<0.05) for storage root yield. Results indicated AMMI analysis as an efficient tool for the evaluation of phenotypic adaptability and stability of cassava clones and IAC 190 as the most promising clone.