Since much of the flow abstracted from the River Indus for irrigation originates in the Himalayas, Karakoram and Hindu Kush Mountains, an understanding of hydrological regimes of mountain rivers is essential for water resources management in Pakistan. Broad characteristics of hydrological regimes are investigated using streamflow data from nineteen long-period stations in terms of annual and seasonal runoff. Regression between climatic variables and streamflow for three key basins, the River Hunza, River Astore and Khan Khwar have first been carried out followed by regional analysis of twelve further basins. Analysis shows distinct hydrological regimes with summer volume governed by: melt of glaciers and permanent snow (thermal control in the current summer), melt of seasonal snow (control by preceding winter and spring precipitation), or winter and monsoon rainfall (precipitation control in current season). Satisfactory levels of correlation were achieved between streamflow and measurements of temperature and precipitation at valley sites, which offer promise as a basis for assessing seasonal flow volumes. They also suggest the possibility of extending the flow record back on the basis of historical climatic records, which commence early in the twentieth century.