The study objective was to investigate whether ultrasound (US) monitoring is essential during treatment with clomiphene citrate (CC) for ovulation induction, as recommended by the Royal College of Obstetricians and Gynaecologists (RCOG) and the National Institute for Clinical Excellence (NICE). We performed a systematic review of all studies investigating the effects of US in the treatment of ovulatory dysfunction with CC. The main objective of this review was to investigate whether US monitoring during CC treatment reduced multiple pregnancy rates. There was insufficient evidence to suggest that US monitoring reduces multiple pregnancy rates or improves pregnancy rates. On the other hand, no indication that treatment with CC is safe without US monitoring was identified. The small number of relevant studies and the heterogeneity observed in the methodologies of each study prohibit reliable conclusions to be drawn. There is currently no basis for amending the evidence base (good-practice points) used in the RCOG and NICE guidelines, which recommend the use of US to monitor the ovaries during stimulation with CC.