The long-term photometric behaviour of the triple system DH Leonis has been studied using the UBV data obtained between 1976 and 1990. The amplitude of the long-term brightness change is about 0.45 magnitudes in V, with an estimated cycle length of 8 to 14 years, whereas the amplitude of the rotational modulation is about 0.15 magnitudes. In terms of starspots this means that the variation of spot coverage with longitude (and latitude) at a given time is less than the variation for the whole star over longer intervals of time. During minimum light the effective spotted area covers about 60% of the surface. The average B - V colour of the system is correlated with the average brightness; the change in B - V corresponds to a change of about two spectral subtypes. It is found that there is more blue light in the system, especially during spot maximum, than expected from the spectral types of the components. Possible causes are discussed. The position of the components in the HR diagram is also discussed.