The self-rooted plum genotype ‘Mrkosljiva’ was first selected as it was devoid of Sharka leaf symptoms during the five-year investigation (2009-2014), which was then confirmed by negative ELISA tests. Hence, the aim of the study was to investigate the biochemical variability of the autochthonous ‘Mrkosljiva’ plum genotype, based on its sugar, acid and phenolic compounds content during three years. In 2010 and 2011, the plums tasted sweet with favourable sugar: acid ratios of 55:1 to 65:1. These plum fruits were collected at the full ripeness stage from an extensive orchard located in northeastern Bosnia and Herzegovina (45 °N). HPLC analysis identified the following polyphenolic compounds, chlorogenic acid, cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, neochlorogenic acid, quercetin-3-O-galactoside and quercetin-3-O-rutinoside in all three evaluated years (2009-2011), but in different amounts, depending on the environmental conditions of each year. In 2009, the plums were healthier in terms of a three-fold greater phenol content compared to the other two growing years. In this year (2009), protocatechulic acid was detected, whereas catechin, procyanidin B1, procyanidin B2 and quercetin-3-O-rhamnoside were not detected. The combination of high phenol and sugar content in ‘Mrkosljiva’ provides healthy and tasty plums suitable primarily for processing, and due to their size to a lesser extent, for fresh fruit marketing.