In general, the disclosure is directed to devices, systems, and techniques for delivering electrical stimulation to a patient with varying pulse frequencies within each burst of pulses. The pulse frequency variation within each burst of pulses may be between approximately 20 Hz and 40 Hz. In some examples, the pulse frequency may be increased, decreased, or polynomially varied within each burst. In other examples, the frequency of intrinsic nerve impulses may be detected and used to deliver pulses with the detected frequency or an inverse of the detected frequency. Electrical stimulation therapy with intra-burst pulse frequency variation may alleviate bladder dysfunction, bowel dysfunction, pain or other disorders.