Diffuse scattering from crystals containing dislocation loops has been calculated. An emphasis was made to reduce numerical computation of lattice sums by an appropriate summing procedure and by limitation of the summation volume by a smooth damping function. The fundamental details of the scattering pattern are discussed in relation to various analytical schemes. Detailed examples are given for circular loops on {111} planes in an elastically isotropic fcc crystal. Characteristic differences are shown between perfect and faulted loops and between vacancy- and interstitial-type loops. Procedures for quantitative determination of loop sizes and concentrations are discussed.