The US is seeing steep decline in measured TV viewing by younger age-groups and rapid increase in digital media adspend, prompting fears about the future of TV ad revenues across the major broadcasters and cable networks. The UK has seen similar trends, prompting suggestions that it will see similar effects. However, comparison of US and UK TV ad revenue trends since 2000 shows big differences in the underlying growth rates after taking economic factors into account. These undermine the inference that the decline in viewing and rise in digital adspend will have similar effects on either side of the Atlantic. Examination of the US and UK TV ad markets further points to big differences across a raft of major variables relating to supply and airtime trading practice, such as can be expected to yield very different outcomes with respect to TV ad revenue growth.