The subsistence production is chosen by farmers because it is subjectively the best option. However, subsistence farming on small and fragmented plots risks not reaching even farmers’ own food requirements, let alone producing a surplus. Therefore, it would have been expected that farmers would be commercialising production of profitable food crops. One of the more profitable food crops than many others as studies show is round potato (Solanum tuberosum). Nonetheless, the extent to which farmers have commercialised round potato production was not known. This study was then undertaken to fill this knowledge gap by analysing the proportion of land allotted to round potato production and the extent to which the crop was oriented towards the market by using the commercialisation index. A sample of 510 farmers was visited from three districts of the southern highlands of Tanzania. Results showed that round potato production was highly commercialised. This was evidence by the proportion of land that was allotted for round potato cultivation and the commercialisation index. About 20 to 67% of the total land under cultivation was allotted to round potato production and about 88% of the produce was sold. However, both the cultivated land and output per capita were small.