Nausea and vomiting of pregnancy (NVP) affects 80% of pregnancies. Its severe form, hyperemesis gravidarum (HG), results in dehydration, electrolyte imbalance, the need for hospitalisation and can, rarely, be fatal. This was a prospective, open-labelled, controlled, interventional study to evaluate the effectiveness of pre-emptive treatment of NVP symptoms in women who experienced severe NVP or HG in their previous pregnancy. Twenty-five women who reported severe symptoms of NVP with or without HG in their previous pregnancy were recruited and counselled to commence the use of antiemetics as soon as they became aware of the present pregnancy, and no later than the beginning of symptoms. They were followed-up prospectively through the index pregnancy for symptoms of NVP, and were counselled continuously as to how to modify antiemetic doses based on symptoms. A comparison group consisted of randomly selected women also counselled by us for NVP, who had also had severe NVP in the previous pregnancy, but who did not call before a planned pregnancy and thus could not be offered pre-emptive therapy. The recruited women commenced pre-emptive drug therapy for NVP before conception or up to 7 weeks' gestation, before the appearance of NVP symptoms in all cases. In comparison to the previous pregnancy, only eight of these 18 women experienced a HG again in the index pregnancy (P = 0.01). The majority of study the women had an improvement in severity of NVP symptoms compared to the previous pregnancy. In the comparison group (n = 35), symptoms in the index pregnancy remained severe in 28 cases (80%), decreased to moderate in six (16.6%) and decreased to mild in five cases (13.9%). There were five cases of HG in the previous pregnancy and three in the index pregnancy. The pre-emptive group was improved significantly compared to the control group (P = 0.01). Pre-emptive symptom management appears to be effective in preventing severe NVP in general, and HG in particular. Women who have experienced severe NVP in a previous pregnancy may benefit from taking antiemetics before, or immediately at the start of symptoms in a subsequent pregnancy.