Abstract Background Slum dwellers display specific traits when it comes to disclosing their illnesses to professionals. The resulting actions lead to poor health-seeking behaviour and underutilisation of existing formal health facilities. The ways that slum people use to communicate their feelings about illness, the type of confidants that they choose, and the supportive and unsupportive social and cultural interactions to which they are exposed have not yet been studied in the Indian context, which constitutes an important knowledge gap for Indian policymakers and practitioners alike. To that end, this study examines the patterns of illness disclosure in Indian slums and the underpinning factors which shape the slum dwellers’ disclosing attitude. Methods In-depth, semi-structured interviews were conducted among 105 men and 113 women who experienced illness in the year prior to the study period. Respondents were selected from four urban slums in two Indian cities, Bangalore and Kolkata. Results Findings indicate that women have more confidants at different social levels, while men have a limited network of disclosures which is culturally and socially mediated. Gender role limitations, exclusion from peer groups and unsupportive local situations are the major cause of disclosure delay or non-disclosure among men, while the main concerns for women are a lack of proper knowledge about illness, unsupportive responses received from other people on certain occasions, the fear of social stigma, material loss and the burden of the local situation. Prompt sharing of illness among men is linked with prevention intention and coping with biological problems, whereas factors determining disclosure for women relate to ensuring emotional and instrumental safety, preventing collateral damage of illness, and preventing and managing biological complications. Conclusions The findings reveal that patterns of disclosure are not determined by the acknowledgment of illness but largely depend on the interplay between individual agency, disclosure consequences and the socio cultural environment. The results of this study can contribute significantly to mitigating the pivotal knowledge gap between health policymakers, practitioners and patients, leading to the formulation of policies that maximise the utilisation of health facilities in slums.