Successful plum production requires cultivars well adapted to the specific growing conditions in the area of production. Due to the interaction between environment and genotype, it is very important to evaluate preliminarily the agronomical and pomological performance of all newly released cultivars in the areas in which they will be cultivated. During the period 1997–2007, the suitability of 15 European and 27 Japanese plum cultivars to cultivation in the Po Valley was observed, as was the influence of year on the main agronomical and pomological traits in plum. Bloom date, yield efficiency, size and soluble sugars content showed great variability across years in both plum species. Winter temperatures, particularly those of the last week of February, had the greatest effect on bloom date. This study confirmed the greater suitability of European plum in northern Italy relative to Japanese plum, even for the most recently introduced cultivars, which had more variable results across years. Within the Japanese group, only ‘Obilnaja’had constant high productivity even in years with unfavourable climatic conditions. Of the 42 cultivars in the trial, the Japanese ‘DOFI Sandra®’,‘Shiro’,‘Anne Gold*’,‘Blackamber’,‘Fortune’,‘Friar’,‘Golden Plumza*’,‘Green Sun*’,‘TC Sun*’,‘Angeleno®*’,‘Autumn Giant®’and the European ‘Firenze 90*’,‘Liablù’,‘Empress’,‘Grossa di Solarolo’,‘Stanley’and ‘President’were most suitable for cultivation in Emilia Romagna.