Due to their high homologous temperature, eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions. In this study, superposition of fatigue and creep deformation and damage under isothermal conditions in rapidly solidified 63Sn-37Pb with and without reflow and conventional 63Sn-37Pb solder alloy is investigated. For strain-controlled fatigue with mean strain, damage is considered in terms of stress relaxation and cyclic softening. For stress-controlled fatigue with mean stress, the fatigue life is modeled with a cycle-time fraction damage law determined from creep rupture and fatigue life data. The nature of damage was investigated by metallographic examination, cavitation measurements, and fractographic observations. The extent of individual creep and fatigue contributions to the overall life and nature of superposition of creep and fatigue is discussed.