Background Over recent decades there has been considerable mental health research in Sierra Leone but little on local conceptualisations of mental health conditions. Understanding these is crucial both for identifying the experienced needs of the population and utilising relevant community-based resources to address them. This study took a grounded approach to identify the ways in which adults in Sierra Leone express psychological distress. Methods Rapid ethnographic methods deployed included 75 case study interviews with community members, 12 key informant (KI) pile sorts and 55 KI interviews. Thematic analysis of data was supported by frequency analysis and multi-dimensional scaling. Results Thirty signs of distress were identified. The only consistent ‘syndrome’ identified with respect to these was a general concept of crase, which referred to psychosis-related presentation but also a wide range of other signs of distress. We did not find consensus on locally defined concepts for mild-moderate forms of mental disorder: people use multiple overlapping signs and terms indicating psychological distress. Conclusions Analysis supports calls to view mental health problems as a ‘continuum of distress’ rather than as discrete categories. This framing is coherent with opportunities for prevention and response in Sierra Leone which do not focus primarily on formal healthcare service providers but rather involve a range of community-based actors. It also enables attention to be paid to the identification of milder signs of distress with a view to early response and prevention of more severe mental health problems.