Approximately 8 to 14 % of women diagnosed with a pregnancy of unknown location (PUL) at their first ultrasound are subsequently found to have an ectopic pregnancy (EP). EP is the leading cause of maternal mortality in the first trimester and therefore the diagnosis of EP without delay in women with a PUL is important in the prevention of the serious complications associated with this condition. However, follow up for women with a PUL (i.e. repeat blood tests +/- ultrasounds) is costly and contributes to maternal anxiety. Recent research has centered on identifying a biochemical serum marker that can distinguish between early intra- and extra- uterine pregnancies. The identification of such a biomarker(s) may result in a reduction in both the healthcare costs and maternal morbidity associated with the delayed diagnosis of EP. This review covers the recently published literature examining the search for an accurate biomarker(s) for the diagnosis of EP in women with a PUL. Although there is not a single biomarker to identify EPs in the PUL population, diagnostic strategies using serum hCG ratios either alone or incorporated into logistic regression models seem to have the best diagnostic performance in case of EP.