A study has been made of the probabilities of marriage of females and males aged 15–49 (either as a whole or in 5-year age groups) in two Outer Hebridean islands, Harris and Barra. The results were compared with ages of marriage and with the frequencies of permanent celibacy. The marriages took place between 1861 and 1990.

Median ages of marriage rose to maxima in the 1930s and 1940s, then fell steeply, levelling out latterly. Permanent celibacy was consistently high among females, but rose from much lower levels in males to maxima in the 1970s and 1980s. It is concluded that in these populations age at marriage and the extent of permanent celibacy are largely independent of one another.

In both islands the overall probabilities of females marrying fell until the 1920s, and then rose. The last decades showed stability (Barra) and a fall (Harris). Males showed only slight falls to about 1910; data were absent for between 1911 and 1960, but subsequently there was little rise in probability.

These overall changes seemed to be associated with reciprocal variations in probabilities in the younger and older age groups. Declining overall probabilities were associated with declines in younger and increases in older age-group probabilities, and vice versa.

Non-parametric correlations between median ages of marriage and probability of marriage were negative and generally significant for the 15–19 age group. Among the older age groups coefficients were generally positive.

There was some evidence of an association between probability of marriage and sex ratio in any group of potential mates. The effect appeared more marked among 15- to 19-year-old females.

Local factors which might explain at least part of the decline in nuptiality for the greater part of the period under study include the decline in the fishing industry and the ‘land hunger’ which existed until the late 1920s. This decline is interpreted as a ‘Malthusian’ response to economic and social conditions, but it coexisted with a ‘neo-Malthusian’ strategy, in the shape of declining marital fertility. The ‘Malthusian’strategy seems to have been largely abandoned around the 1950s, but it may have reappeared during the 1980s.