Nettle root is recommended for complaints associated with benign prostatic hyperplasia (BPH). We therefore conducted a comprehensive review of the literature to summarise the pharmacological and clinical effects of this plant material. Only a few components of the active principle have been identified and the mechanism of action is still unclear. It seems likely that sex hormone binding globulin (SHBG), aromatase, epidermal growth factor and prostate steroid membrane receptors are involved in the anti-prostatic effect, but less likely that 5alpha-reductase or androgen receptors are involved. Extract and a polysaccharide fraction were shown to exert anti-inflammatory activity. A proprietary methanolic nettle root extract and particular fractions inhibited cell proliferation. Isolated lectins (UDA) were shown to be promising immunomodulatory agents, having also anti-viral and fungistatic effects. However, despite these in vitro studies it is unclear whether the in-vitro or animal data are a surrogate for clinical effects. The clinical evidence of effectiveness for nettle root in the treatment of BPH is based on many open studies. A small number of randomised controlled studies indicate that a proprietary methanolic extract is effective in improving BPH complaints. However, the significance and magnitude of the effect remains to be established in further confirmatory studies before nettle root treatment may be accepted in the guidelines for BPH treatment. The risk for adverse events during nettle root treatment is very low, as is its toxicity. Pre-clinical safety data remain to be completed.