While young couples in Western societies generally form a new household, in low-income societies new unions are often incorporated into existing households. However, there is a growing tendency in the nuclearization of households as intergenerational coresidence is undermined by growing wage labour opportunities that provide incentives for rural–urban migration and because small nuclear families adapt better to urban societies characterized by high geographic and social mobility. The objective of this paper is therefore to jointly study for a selection of low- to middle-income countries the socioeconomic and demographic conditions of women aged 15–34 and their partners in relation to their household patterns with particular interest in the comparison of nuclear and extended households. The analysis will mainly rely on data from the Integrated Public Use of Microdata Series International database (https://international.ipums.org/international/) from which census samples for the last two or latest available census rounds for 18 countries have been extracted. Results showed that women being of older age (within the 15–34 range) and at the same time having attained at least primary school education, having a husband who does not work in the primary sector and who is neither much older nor much younger were all associated with living in a nuclear household. However, individual factors explained only a small part of the overall variation in the household arrangements of young couples, suggesting that differences between countries in these dimensions do not explain much of the difference in household structure. Rather, societal indicators like economic development and the average age at marriage – that were significant in our models – may explain better the overall slow transition towards the nuclear family.