There is a lack of data on the occurrence of pharmaceuticals in estuaries worldwide, with little understanding of their temporal and spatial variations globally. Ibuprofen, paracetamol, diclofenac, trimethoprim and citalopram were measured in twelve estuaries in the UK. Initially, these compounds were monitored in the Humber Estuary, where samples were taken every two months over a twelve month period in order to assess their spatial and temporal variations. Ibuprofen was found at some of the highest concentrations ever measured in an estuary globally (18 – 6297ng l-1), with paracetamol also measured at relatively high concentrations (4 – 917 ng l-1) in comparison to the other compounds. In terms of spatial distribution, a pattern was observed, where highest concentrations were found at a site where wastewater is discharged, whilst compound concentrations were often lower upstream and downstream of this site. The downstream profile of pharmaceuticals differed temporally with concentrations highest downstream when input from wastewater effluent was highest. Eleven further estuaries were sampled around the UK in order to put the occurrence of pharmaceuticals seen in the Humber Estuary into a wider context. Pharmaceutical concentrations in the other estuaries sampled were less than 210 ng l-1, but, again, ibuprofen and paracetamol were found at concentrations higher than other compounds, whereas diclofenac and citalopram were absent from many estuaries. The Humber, which is the receiving environment for the sewage effluent for approximately 20% (13.6 million people) of the population of England, was observed to have the highest overall concentration of pharmaceuticals in contrast to the other estuaries sampled, thereby representing a worst case scenario for pharmaceutical pollution.