Background: Psychotherapy and mental health services in Nairobi's public hospitals are increasing. Rather than prematurely imposing psychotherapy protocols developed in Western countries to Kenya, we argue that first studying psychological interventions as they are practiced may generate understanding of which psychological problems are common, what interventions therapists use, and what seems to be effective in reducing psychiatric problems in a lower and middle income country like Kenya. Method: We present preliminary findings from a process-outcome study involving 345 patients from two public institutions, Kenyatta National and Mathare National Hospitals. We asked our patients to fill out a brief personal information questionnaire, Clinical Outcomes in Routine Evaluation-Outcome Measure (Evans et al. in Br J Psychiatry 180:51–60, 2002, and the Session Alliance Inventory (Falkenström et al. in Psychol Assess 27:169–183, 2015) after each session. We present descriptives for CORE-OM, patient-therapist concordance on the SAI, and using longitudinal mixed-effects model, test change in CORE-OM over time with various therapy and patient factors as predictors in regression analyses. Results: The majority of patients who attended the outpatient care clinics were young males. Our regression analysis suggested that patients with depression reported higher initial distress levels (2.75 CORE-OM scores, se = 1.11, z = 2.48, p = 0.013, 95% CI 0.57–4.93) than patients with addictions, anxiety, or psychosis. Older clients improved slower (0.08 CORE-OM scores slower improvement per session per year older age; se = 0.03, z = 3.02 p = 0.003, 95% CI 0.03, 0.14). Female patients reported higher initial distress than men (2.62 CORE-OM scores, se = 1.00, z = 2.61, p = 0.009, 95% CI 0.65, 4.58). However, interns had patients who reported significantly higher initial distress (3.24 CORE-OM points, se = 0.90, z = 3.60, p < 0.001, 95% CI 1.48, 5.00), and improved more over time (− 1.20 CORE-OM scores per session, se = 0.51, z = − 2.35, p = 0.019, 95% CI − 2.20, − 0.20) than patients seeing mental health practitioners. The results showed that at average alliance, CORE-OM decreased by 1.74 points per session (se = 0.21, p < 0.001). For each point higher on the SAI at session 2, the CORE-OM decreased by an additional 0.58 points per session (se = 0.25, p = 0.02). Discussion: Our objective was to study psychotherapies as they are practiced in naturalistic settings. The overall significant finding is that our participants report improvement in their functioning mental health condition and distress reduced as psychotherapy progressed. There were many more male than female participants in our sample; younger patients improved more than older ones; and while interns had patients with higher distress, their patients improved better than those patients attended by professionals. Conclusions: These are preliminary observations to consider for a larger sample follow-up study. Before changing practices, evaluating the existing practices by mapping clinical outcomes is a helpful route. [ABSTRACT FROM AUTHOR]