This paper studies the determinants and behavior of outstanding mortgage loan to value (LTV) ratios for a panel data set of 5,179 households over the period 1992-2005. We find that outstanding LTVs are driven by household characteristics, life-cycle effects and mortgage type characteristics. LTV declines with the time elapsed since mortgage commencement, but its level is consistently higher (by around 10%) for non-repayment mortgages (such as interest-only or endowment mortgages) than for repayment mortgages (such as linear or annuity mortgages). The difference results from higher debt capacity associated with the possibility of deferring the principal repayment for non-repayment mortgages. Our results indicate that the recent proliferation of non-repayment mortgages is driven by tightening financing constraints due to declining affordability in the housing market and that the overall quality of outstanding mortgages has substantially deteriorated over the last decade.