One of the major constraints of cassava as a crop is its perishability. Physiological deterioration, parenchymal blue-black vascular streaking, often starts within 24 h after harvest. This paper presents the results of a detailed study of the effects of pre-harvest pruning upon post-harvest physiological deterioration (PPD) and some other quality characteristics. Six cultivars, grown at CIAT (Centro International de Agricultura Tropical), with varying intrinsic susceptibility to PPD), were assessed at pruning-harvest intervals of 0, 2, 4, 6, 8, 10, 15, 20, 25, 28 and 39 days. After harvesting, the roots were analysed. For the unpruned plants a low susceptibility was found to coincide with a low dry matter content and a high sugar content. After pruning, the susceptibility for all cultivars was drastically reduced, reaching a minimum of around 25% of the original value for a pruning-harvest interval of up to 25 days. Beyond this interval the plants slowly develop new leaf canopy, normal assimilation sets in again and the starch content increases. Analysis of the cassava roots revealed a relationship between the combined sugar and starch contents and the interval duration, and that sugar and starch contents were inversely related to each other. The sugar content increased with the interval period, probably as a result of starch hydrolysis. Other properties such as the contents of dry matter, cyanogen, scopoletin, amylose and reducing sugars and the starch pasting properties were not affected by pruning to a comparable, interval-dependent, extent. It is concluded that the sugar content, ie the sugaristarch ratio, of cassava roots is positively related to their resistance to post-harvest physiological deterioration.